Hollow Micro/Nanostructured Ceria-Based Materials: Synthetic Strategies and Versatile Applications

Recent Advances of CeO2-Based Composite Materials for Photocatalytic Applications

Photocatalysis has the advantages of practical, sustainable and environmental protection, so it plays a significant role in energy transformation and environmental utilization. CeO2 has attracted widespread attention for its unique 4 f electrons, rich defect structures, high oxygen storage capacity and great chemical stability. In this paper, we review the structure of CeO2 and the common methods for the preparation of CeO2-based composites in the first part. In particular, we highlight the co-precipitation method, template method, and sol-gel method methods. Then, in the second part, we introduce the application of CeO2-based composites in photocatalysis, including photocatalytic CO2 reduction, hydrogen production, degradation, selective organic reaction, and photocatalytic nitrogen fixation. In addition, we discuss several modification techniques to improve the photocatalytic performance of CeO2-based composites, such as elemental doping, defect engineering, constructing heterojunction and morphology regulation. Finally, the challenges faced by CeO2-based composites are analyzed and their development prospects are prospected. This review provides a systematic summary of the recent advance of CeO2-based composites in the field of photocatalysis, which can provide useful references for the rational design of efficient CeO2-based composite photocatalysts for sustainable development.

CeO2 In Situ Growth on Red Blood Cell Membranes: CQD Coating and Multipathway Alzheimer's Disease Therapy under NIR

Alzheimer's disease (AD) has a complex etiology and diverse pathological processes. The therapeutic effect of single-target drugs is limited, so simultaneous intervention of multiple targets is gradually becoming a new research trend. Critical stages in AD progression involve amyloid-β (Aβ) self-aggregation, metal-ion-triggered fibril formation, and elevated reactive oxygen species (ROS). Herein, red blood cell membranes (RBC) are used as templates for the in situ growth of cerium oxide (CeO2) nanocrystals. Then, carbon quantum dots (CQDs) are encapsulated to form nanocomposites (CQD-Ce-RBC). This strategy is combined with photothermal therapy (PTT) for AD therapy. The application of RBC enhances the materials' biocompatibility and improves immune evasion. RBC-grown CeO2, the first application in the field of AD, demonstrates outstanding antioxidant properties. CQD acts as a chelating agent for copper ions, which prevents the aggregation of Aβ. In addition, the thermal effect induced by near-infrared laser-induced CQD can break down Aβ fibers and improve the permeability of the blood-brain barrier. In vivo experiments on APP/PS1 mice demonstrate that CQD-Ce-RBC combined with PTT effectively clears cerebral amyloid deposits and significantly enhances learning and cognitive abilities, thereby retarding disease progression. This innovative multipathway approach under light-induced conditions holds promise for AD treatment.

The Structures and Compositions Design of the Hollow Micro-Nano-Structured Metal Oxides for Environmental Catalysis

In recent decades, with the rapid development of the inorganic synthesis and the increasing discharge of pollutants in the process of industrialization, hollow-structured metal oxides (HSMOs) have taken on a striking role in the field of environmental catalysis. This is all due to their unique structural characteristics compared to solid nanoparticles, such as high loading capacity, superior pore permeability, high specific surface area, abundant inner void space, and low density. Although the HSMOs with different morphologies have been reviewed and prospected in the aspect of synthesis strategies and potential applications, there has been no systematic review focusing on the structures and compositions design of HSMOs in the field of environmental catalysis so far. Therefore, this review will mainly focus on the component dependence and controllable structure of HSMOs in the catalytic elimination of different environmental pollutants, including the automobile and stationary source emissions, volatile organic compounds, greenhouse gases, ozone-depleting substances, and other potential pollutants. Moreover, we comprehensively reviewed the applications of the catalysts with hollow structure that are mainly composed of metal oxides such as CeO2, MnOx, CuOx, Co3O4, ZrO2, ZnO, Al3O4, In2O3, NiO, and Fe3O4 in automobile and stationary source emission control, volatile organic compounds emission control, and the conversion of greenhouse gases and ozone-depleting substances. The structure-activity relationship is also briefly discussed. Finally, further challenges and development trends of HSMO catalysts in environmental catalysis are also prospected.

Engineering Nanozymes for Tumor Therapy via Ferroptosis Self-Amplification

Ferroptosis induction is an emerging strategy for tumor therapy. Reactive oxygen species (ROS) can induce ferroptosis but are easily consumed by overexpressed glutathione (GSH) in tumor cells. Therefore, achieving a large amount of ROS production in tumor cells without being consumed is key to efficiently inducing ferroptosis. In this study, a self-amplifying ferroptosis-inducing therapeutic agent, Pd@CeO2-Fe-Co-WZB117-DSPE-PEG-FA (PCDWD), is designed for tumor therapy. PCDWD exhibits excellent multi-enzyme activities due to the loading of Fe-Co dual atoms with abundant active sites, including peroxidase-like enzymes, catalase-like enzymes, and glutathione oxidases (GSHOx), which undergo catalytic reactions in the tumor microenvironment to produce ROS, thereby inducing ferroptosis. Furthermore, PCDWD can also deplete GSH in tumor cells, thus reducing the consumption of ROS by GSH and inhibiting the expression of GSH peroxidase 4. Moreover, the photothermal effect of PCDWD can not only directly kill tumor cells but also further enhance its own enzyme activities, consequently promoting ferroptosis in tumor cells. In addition, WZB117 can reduce the expression of heat shock protein 90 by inhibiting glucose transport, thereby reducing the thermal resistance of tumor cells and further improving the therapeutic effect. Finally, X-ray computed tomography imaging of PCDWD guides it to achieve efficient tumor therapy.

Multifunctional Nanocarrier for Synergistic Treatment of Alzheimer's Disease by Inhibiting β-Amyloid Aggregation and Scavenging Reactive Oxygen Species

The excessive depositions of β-amyloid (Aβ) and abnormal level of reactive oxygen species (ROS) are considered as the important pathogenic factors of Alzheimer's disease (AD). Strategies targeting only one of them have no obvious effects in clinic. In this study, a multifunctional nanocarrier CICe@M-K that crosses the blood-brain barrier (BBB) efficiently was developed for inhibiting Aβ aggregation and scavenging ROS synchronously. Antioxidant curcumin (Cur) and photosensitizer IR780 were loaded in mesoporous silica nanomaterials (MSNs). Their surfaces were grafted with cerium oxide nanoparticles (CeO2 NPs) and a short peptide K (CKLVFFAED). Living imaging showed that CICe@M-K was mainly distributed in the brain, liver, and kidneys, indicating CICe@M-K crossed BBB efficiently and accumulated in brain. After the irradiation of 808 nm laser, Cur was continuously released. Both of Cur and the peptide K can recognize and bind to Aβ through multiple interaction including π-π stacking interaction, hydrophobic interaction, and hydrogen bond, inhibiting Aβ aggregation. On the other hand, Cur and CeO2 NPs cooperate to relieve the oxidative stress in the brains by scavenging ROS. In vivo assays showed that the CICe@M-K could diminish Aβ depositions, alleviate oxidative stress, and improve cognitive ability of the APP/PS1 AD mouse model, which demonstrated that CICe@M-K is a potential agent for AD treatment.

In Vitro Synergistic Photodynamic, Photothermal, Chemodynamic, and Starvation Therapy Performance of Chlorin e6 Immobilized, Polydopamine-Coated Hollow, Porous Ceria-Based, Hypoxia-Tolerant Nanozymes Carrying a Cascade System

A synergistic therapy agent (STA) with photothermal, photodynamic, chemodynamic, and starvation therapy (PTT, PDT, CDT, and ST) functions was developed. Hollow, mesoporous, and nearly uniform CeO2 nanoparticles (H-CeO2 NPs) were synthesized using a staged shape templating sol-gel protocol. Chlorin e6 (Ce6) was adsorbed onto H-CeO2 NPs, and a thin polydopamine (PDA) layer was formed on Ce6-adsorbed H-CeO2 NPs. Glucose oxidase (GOx) was bound onto PDA-coated Ce6-adsorbed H-CeO2 NPs to obtain the targeted STA (H-CeO2@Ce6@PDA@GOx NPs). A reversible photothermal conversion behavior with the temperature elevations up to 34 °C was observed by NIR laser irradiation at 808 nm. A cascade enzyme system based on immobilized GOx and intrinsic catalase-like activity of H-CeO2 NPs was rendered on STA for enhancing the effectiveness of PDT by elevation of ROS generation and alleviation of hypoxia in a tumor microenvironment. Glucose-mediated generation of highly toxic hydroxyl radicals (·OH) was evaluated for CDT. The effectiveness of PDT on glioblastoma T98G cells was markedly enhanced by O2 generation started by the decomposition of glucose. A similar increase in cell death was also observed when ST and CDT functions were enhanced by photothermal action. The viability of T98G cells decreased to 10.6% by in vitro synergistic action including ST, CDT, PDT, and PTT without using any antitumor agent.

Pathogen-Activated Macrophage Membrane Encapsulated CeO2-TCPP Nanozyme with Targeted and Photo-Enhanced Antibacterial Therapy

Nanozymes with peroxidase-mimic activity have recently emerged as effective strategies for eliminating infections. However, challenges in enhancing catalytic activities and the ability to target bacteria have hindered the broader application of nanozymes in bacterial infections. Herein, a novel nanozyme based on mesoporous CeO2 nanosphere and meso-tetra(4-carboxyphenyl)porphine (TCPP) encapsulated within pathogen-activated macrophage membranes, demonstrates photodynamic capability coupled with photo-enhanced chemodynamic therapy for selective and efficient antibacterial application against infected wounds. Interestingly, the expression of Toll-like receptors accordingly upregulates when macrophages are co-cultured with specific bacteria, thereby facilitating to recognition of the pathogen-associated molecular patterns originating from bacteria. The CeO2 not only serve as carriers for TCPP, but also exhibit intrinsic peroxidase-like catalytic activity. Consequently, Staphylococcus aureus (S. aureus)-activated macrophage membrane-coated CeO2-TCPP (S-MM@CeO2-TCPP) generated singlet oxygen, and simultaneously promoted photo-enhanced chemodynamic therapy, significantly boosting reactive oxygen species (ROS) to effectively eliminate bacteria. S-MM@CeO2-TCPP specifically targeted S. aureus via Toll-like receptor, thereby directly disrupting bacterial structural integrity to eradicate S. aureus in vitro and relieve bacteria-induced inflammation to accelerate infected wound healing in vivo. By selectively targeting specific bacteria and effectively killing pathogens, such strategy provides a more efficient and reliable alternative for precise elimination of pathogens and inflammation alleviation in microorganism-infected wounds.

The Role of Reactive Oxygen Species in Alzheimer's Disease: From Mechanism to Biomaterials Therapy

Alzheimer's disease (AD) is a chronic, insidious, and progressive neurodegenerative disease that remains a clinical challenge for society. The fully approved drug lecanemab exhibits the prospect of therapy against the pathological processes, while debatable adverse events conflict with the drug concentration required for the anticipated therapeutic effects. Reactive oxygen species (ROS) are involved in the pathological progression of AD, as has been demonstrated in much research regarding oxidative stress (OS). The contradiction between anticipated dosage and adverse event may be resolved through targeted transport by biomaterials and get therapeutic effects through pathological progression via regulation of ROS. Besides, biomaterials fix delivery issues by promoting the penetration of drugs across the blood-brain barrier (BBB), protecting the drug from peripheral degradation, and elevating bioavailability. The goal is to comprehensively understand the mechanisms of ROS in the progression of AD disease and the potential of ROS-related biomaterials in the treatment of AD. This review focuses on OS and its connection with AD and novel biomaterials in recent years against AD via OS to inspire novel biomaterial development. Revisiting these biomaterials and mechanisms associated with OS in AD via thorough investigations presents a considerable potential and bright future for improving effective interventions for AD.

Stabilizing Undercoordinated Zn Active Sites through Confinement in CeO2 Nanotubes for Efficient Electrochemical CO2 Reduction

Zn-based catalysts hold great potential to replace the noble metal-based ones for CO2 reduction reaction (CO2 RR). Undercoordinated Zn (Znδ+ ) sites may serve as the active sites for enhanced CO production by optimizing the binding energy of *COOH intermediates. However, there is relatively less exploration into the dynamic evolution and stability of Znδ+ sites during CO2 reduction process. Herein, we present ZnO, Znδ+ /ZnO and Zn as catalysts by varying the applied reduction potential. Theoretical studies reveal that Znδ+ sites could suppress HER and HCOOH production to induce CO generation. And Znδ+ /ZnO presents the highest CO selectivity (FECO 70.9 % at -1.48 V vs. RHE) compared to Zn and ZnO. Furthermore, we propose a CeO2 nanotube with confinement effect and Ce3+ /Ce4+ redox to stabilize Znδ+ species. The hollow core-shell structure of the Znδ+ /ZnO/CeO2 catalyst enables to extremely expose electrochemically active area while maintaining the Znδ+ sites with long-time stability. Certainly, the target catalyst affords a FECO of 76.9 % at -1.08 V vs. RHE and no significant decay of CO selectivity in excess of 18 h.

Deep Insight of Design, Mechanism, and Cancer Theranostic Strategy of Nanozymes

Since the discovery of enzyme-like activity of Fe3O4 nanoparticles in 2007, nanozymes are becoming the promising substitutes for natural enzymes due to their advantages of high catalytic activity, low cost, mild reaction conditions, good stability, and suitable for large-scale production. Recently, with the cross fusion of nanomedicine and nanocatalysis, nanozyme-based theranostic strategies attract great attention, since the enzymatic reactions can be triggered in the tumor microenvironment to achieve good curative effect with substrate specificity and low side effects. Thus, various nanozymes have been developed and used for tumor therapy. In this review, more than 270 research articles are discussed systematically to present progress in the past five years. First, the discovery and development of nanozymes are summarized. Second, classification and catalytic mechanism of nanozymes are discussed. Third, activity prediction and rational design of nanozymes are focused by highlighting the methods of density functional theory, machine learning, biomimetic and chemical design. Then, synergistic theranostic strategy of nanozymes are introduced. Finally, current challenges and future prospects of nanozymes used for tumor theranostic are outlined, including selectivity, biosafety, repeatability and stability, in-depth catalytic mechanism, predicting and evaluating activities.

Efficient Exciton Dissociation on Ceria Chelated Cerium-Based MOF Isogenous S-Scheme Photocatalyst for Acetaldehyde Purification

Long-term exposure to low concentration indoor VOCs of acetaldehyde (CH3 CHO) is harmful to human health. Thus, a novel isogenous heterojunction CeO2 /Ce-MOF photocatalyst is synthesized via a one-step hydrothermal method for the effective elimination of CH3 CHO in this work. This CeO2 /Ce-MOF photocatalyst performs well in CH3 CHO removal and achieves an apparent quantum efficiency of 7.15% at 420 nm, which presents ≈6.7 and 3.4 times superior to those generated by CeO2 and Ce-MOF, respectively. The enhanced efficiency is due to two main aspects including i) an effective photocarrier separation ability and the prolonged reaction lifetime of excitons play crucial roles and ii) the formation of an internal electric field (IEF) is sufficient to overcome the considerable exciton binding energy, and increases the exciton dissociation efficiency by up to 50.4%. Moreover, the reasonable pathways and mechanisms of CH3 CHO degradation are determined by in situ DRIFTS analysis and simulated DFT calculations. Those results demonstrated that S-scheme heterojunction successfully increases the efficiency of harmful volatile organic compounds elimination, and it offers essential guidance for designing rare earth-based MOF photocatalysts.

Cellulose acetate/polyurethane blend as support matrix with high optical transparency and improved mechanical properties for photocatalyst CeO2 nanoparticles immobilization

Advanced manufacturing technologies for efficient catalytic materials have triggered the rational design of catalysts as well as extensive investigation into preparative methodologies. Herein, we report the preparation of new versatile cellulose acetate/polyurethane (CA/PU) blends for efficient immobilization of CeO2 nanoparticles, the appropriate composition of polymer mixture being chosen after rigorous analysis (SEM, FTIR, optical, mechanical). The band gap energy for hybrid films ranged between 3.02 eV and 2.05 eV, the lowest value being measured for the film with Co-doped CeO2 NPs (B3 film). The best results in photodegradation of methylene blue under visible-light irradiation was attained after 50 min for B3 film (rate constant k = 45.34× 10-3 min-1), while the total mineralization of MB in the same conditions as evaluated by HPLC-ESI MS and TOC analyses was achieved after 90 min. Effect of co-ions (SO42-, Cl- or NO3-) on photocatalytic performance was studied, and scavenger tests were used to identify the active species involved in the photocatalytic mechanism. Also, the photocatalytic efficiency of B3 sample was tested for rhodamine B, metronidazole and 4-nitrophenol degradation. Evaluation of the stability and integrity of hybrid film after 5 catalysis cycles reveal that the photocatalytic potential is retained with no substantial structural changes.

Polyoxometalate functionalizing CeO2 hollow nanospheres as enhanced oxidase mimics for ascorbic acid colorimetric sensing

Phosphotungstic acid covered with CeO₂ hollow nanospheres (CeO₂@PTA HNSs) has been successfully prepared by a simple method, serving as highly efficient nanozymes for ascorbic acid (AA) colorimetric sensing. In virtue of the unique hollow nanostructures, oxide defects and synergic effects of CeO₂ and PTA, the proposed CeO₂@PTA HNSs present remarkable intrinsic oxidase-like activity and help capture electrons from 3,3',5,5'-tetramethylbenzidine (TMB). Due to the reducibility of AA, a promising colorimetric sensing platform based on CeO₂@PTA HNSs has been constructed for quantitative analysis of AA. The present colorimetric detection exhibits a low limit of detection, good selectivity and stability, as well as reliability in orange juice and milk. This work provides a simple surface defect engineering to prepare high-performance oxidase mimics in the application of colorimetric biosensing.

Cu-Ce oxide Co-loaded silicon nanocapsules for hydrogen peroxide self-supplied Fenton-like catalysis and synergistically antibacterial therapy

Antibacterial strategies based on reactive oxygen species (ROS) have opened up a new avenue for overcoming the great challenges of antibiotics topic including lack of broad-spectrum antibiotics and the emergence of super-resistant bacteria. Herein, we leveraged a strategy of constructing synergistic catalytic active sites to develop a simple yet efficient Fenton-like active nanocomposite, and investigated its catalysis mechanism and antibacterial performance thoroughly. This strategy provides a new direction for boosting the catalytic activity of nanocomposite catalysts for wide application. Specifically, by uniformly loading copper oxide and ceria onto the surface of silica nanocapsules (SiO₂ NCs), we fabricated a bimetallic oxide nanocomposite Cu_0.75Ce_0.62O₂@SiO₂ NC, which performed superior Fenton-like capability in a wide pH range without additional exogenetic hydrogen peroxide (H₂O₂). Such excellent catalytic activity was originated from the charge interaction between the two metal oxide components, where formation of Cu⁺ and oxygen vacancies (OVs) was mutually reinforcing, resulting in a synergistic effect to produce H₂O₂ and catalyze the generation of •OH under the slight acid condition (pH = 6.0). In view of the outstanding Fenton-like activity, the Cu_0.75Ce_0.62O₂@SiO₂ NC was employed in antimicrobial testing, which demonstrated exceptional high in vitro antimicrobial efficacy against both the S. aureus and E. coli in a neutral environment (pH = 7.4). The excellent performance of the bimetallic nanocomposite Cu_0.75Ce_0.62O₂@SiO₂ NC, including its facile and mild preparation, high water-solubility and stability, superior catalytic and antimicrobial performances, manifests a promising broad-spectrum antibiotic that can be anticipated to deal with the contamination of the environment by bacteria.

Synergistic Effect between Ni and Ce Dual Active Centers Initiated by Activated Fullerene Soot for Electro−Fenton Degradation of Tetracycline

The degradation of a high concentration of organic pollutants has long been a challenge to water restoration, and the development of electro−Fenton catalysis offers a practical approach to solving this problem. In this study, a novel electro−Fenton catalyst, activated fullerene soot−loaded NiO−doped CeO2 (0.4(0.4NiO−CeO2)−AFS) nanoparticles, was prepared through the impregnation of 0.4NiO−CeO2 particles and activated fullerene soot (AFS). When applied for the degradation of 200 mg/L of tetracycline, this catalyst demonstrated a degradation rate as high as 99%. Even after 20 cycles, the degradation rate was more than 80%. Moreover, it was concluded that AFS could initiate the synergistic effect between Ni and Ce dual active centers in the degradation of tetracycline; this can be ascribed to the extremely large specific surface area of AFS.

Hollow Mesoporous Manganese Oxides: Application in Cancer Diagnosis and Therapy

The precision, minimal invasiveness, and integration of diagnosis and treatment are critical factors for tumor treatment at the present. Although nanomedicine has shown the potential in tumor precision treatment, nanocarriers with high efficiency, excellent targeting, controlled release, and good biocompatibility still need to be further explored. Hollow mesoporous manganese oxides nanomaterials (HM-MONs), as an efficient drug delivery carrier, have attracted substantial attention in applications of tumor diagnosis and therapy due to their unique properties, such as tumor microenvironment stimuli-responsiveness, prominent catalytic activity, excellent biodegradation, and outstanding magnetic resonance imaging ability. The HM-MONs can not only enhance the therapeutic efficiency but also realize multimodal diagnosis of tumors. Consequently, it is necessary to introduce applications based on HM-MONs in cancer diagnosis and therapy. In this review, the representative progress of HM-MONs in synthesis is discussed. Then, several promising applications in drug delivery, bio-imaging, and bio-detection are highlighted. Finally, the challenges and perspectives of the anticancer applications are summarized, which is expected to provide meaningful guidance on further research.

Gold Nanorods with Spatial Separation of CeO2 Deposition for Plasmonic-Enhanced Antioxidant Stress and Photothermal Therapy of Alzheimer's Disease

Activities of catalase (CAT) and superoxide dismutase (SOD) of ceria nanoparticles (CeO₂ NPs) provide the possibility for their application in nervous system oxidative stress diseases including Alzheimer's disease (AD). The addition of hot electrons produced by a plasma photothermal effect can expand the photocatalytic activity of CeO₂ to the near-infrared region (NIR), significantly improving its redox performance. Therefore, we coated both ends of gold nanorods (Au NRs) with CeO₂ NPs, and photocatalysis and photothermal therapy in the NIR are introduced into the treatment of AD. Meanwhile, the spatially separate structure enhances the catalytic performance and photothermal conversion efficiency. In addition, the photothermal effect significantly improves the permeability of the blood-brain barrier (BBB) and overcomes the shortcomings of traditional anti-AD drugs. To further improve the therapeutic efficiency, Aβ-targeted inhibitory peptides were modified on the middle surface of gold nanorods to synthesize KLVFF@Au-CeO₂ (K-CAC) nanocomposites. We have verified their biocompatibility and therapeutic effectiveness at multiple levels in vitro and in vivo, which have a profound impact on the research and clinical transformation of nanotechnology in AD therapy.

Nitrogen and sulfur co-doped CeO2 nanorods for efficient photocatalytic VOCs degradation

Nitrogen and sulfur-co-doped ceria with a regular nanorod morphology was prepared by one-step calcination treatment. N and S dopants can generate new impurity level states and promote the photocatalytic performance of CeO2 for VOCs degradation.

Construction of a Mesoporous Ceria Hollow Sphere/Enzyme Nanoreactor for Enhanced Cascade Catalytic Antibacterial Therapy

Nanozyme has been regarded as one of the antibacterial agents to kill bacteria via a Fenton-like reaction in the presence of H₂O₂. However, it still suffers drawbacks such as insufficient catalytic activity in near-neutral conditions and the requirement of high H₂O₂ levels, which would minimize the side effects to healthy tissues. Herein, a mesoporous ceria hollow sphere/enzyme nanoreactor is constructed by loading glucose oxidase in the mesoporous ceria hollow sphere nanozyme. Due to the mesoporous framework, large internal voids, and high specific surface area, the obtained nanoreactor can effectively convert the nontoxic glucose into highly toxic hydroxyl radicals via a cascade catalytic reaction. Moreover, the generated glucose acid can decrease the localized pH value, further boosting the peroxidase-like catalytic performance of mesoporous ceria. The generated hydroxyl radicals could damage severely the cell structure of the bacteria and prevent biofilm formation. Moreover, the in vivo experiments demonstrate that the nanoreactor can efficiently eliminate 99.9% of bacteria in the wound tissues and prevent persistent inflammation without damage to normal tissues in mice. This work provides a rational design of a nanoreactor with enhanced catalytic activity, which can covert glucose to hydroxyl radicals and exhibits potential applications in antibacterial therapy.

Nanostructured Ceria: Biomolecular Templates and (Bio)applications

Ceria (CeO2) nanostructures are well-known in catalysis for energy and environmental preservation and remediation. Recently, they have also been gaining momentum for biological applications in virtue of their unique redox properties that make them antioxidant or pro-oxidant, depending on the experimental conditions and ceria nanomorphology. In particular, interest has grown in the use of biotemplates to exert control over ceria morphology and reactivity. However, only a handful of reports exist on the use of specific biomolecules to template ceria nucleation and growth into defined nanostructures. This review focusses on the latest advancements in the area of biomolecular templates for ceria nanostructures and existing opportunities for their (bio)applications.

Chem-inspired hollow ceria nanozymes with lysosome-targeting for tumor synergistic phototherapy

The precise operation of the hypoxic tumor microenvironment presents a promising way to improve treatment efficacy, in particular in tumor synergistic phototherapy. This work reports an innovative approach to build adenosine triphosphate-modified hollow ceria nanozymes (ATP-HCNPs@Ce6) that manipulate tumor hypoxia to effectively achieve drug delivery. Hollow ceria nanoparticles (HCNPs) exhibit a controllable hollow structure through varying nitric acid concentrations in the nanocomposites. Specifically, ATP modification makes HCNPs exceptionally biocompatible and stable and acts as a regulator of HCNP enzymatic activity. In the stage of drug loading, newly prepared ATP-HCNPs@Ce6 serves as an in situ oxygen-generating agent because of its ability to simulate catalase. Therefore, ATP-HCNPs@Ce6 has adjustable enzymatic properties that act like a "switch" to selectively supply oxygen in response to high levels of hydrogen peroxide expression and the slightly acidic lysosomal environment of the tumor to enhance lysosome-targeted photodynamic therapy. Moreover, the obvious anticancer effects of ATP-HCNPs@Ce6 are demonstrated in vitro and in vivo. Overall, a simple and rapid self-assembly strategy to form and modify multifunctional HCNPs is reported, which may further propel their application in the field of precision tumor treatment.

Antisolvent Route to Ultrathin Hollow Spheres of Cerium Oxide for Enhanced CO Oxidation

Cerium(IV) oxide (CeO₂), or ceria, is one of the most abundant rare-earth materials that has been extensively investigated for its catalytic properties over the past two decades. However, due to the global scarcity and increasing cost of rare-earth materials, efficient utilization of this class of materials poses a challenging issue for the materials research community. Thus, this work is directed toward an exploration of making ultrathin hollow ceria or other rare-earth metal oxides and mixed rare-earth oxides in general. Such a hollow morphology appears to be attractive, especially when the thickness is trimmed to its limit, so that it can be viewed as a two-dimensional sheet of organized nanoscale crystallites, while remaining three-dimensional spatially. This ensures that both inner and outer shell surfaces can be better utilized in catalytic reactions if the polycrystalline sphere is further endowed with mesoporosity. Herein, we have devised our novel synthetic protocol for making ultrathin mesoporous hollow spheres of ceria or other desired rare-earth oxides with a tunable shell thickness in the region of 10 to 40 nm. Our ceria ultrathin hollow spheres are catalytically active and outperform other reported similar nanostructured ceria for the oxidation reaction of carbon monoxide in terms of fuller utilization of cerium. The versatility of this approach has also been extended to fabricating singular or multicomponent rare-earth metal oxides with the same ultrathin hollow morphology and structural uniformity. Therefore, this approach holds good promise for better utilization of rare-earth metal elements across their various technological applications, not ignoring nano-safety considerations.

Photocatalytic degradation of organic dye and tetracycline by ternary Ag2O/AgBr-CeO2 photocatalyst under visible-light irradiation

In this work, CeO2 nanosheets decorated with Ag2O and AgBr are successfully fabricated via a simple sediment-precipitation method. The as-prepared ternary Ag2O/AgBr-CeO2 composite with double Z-scheme construction was analyzed by various analytical techniques. Ag nanoparticles (NPs) used as the electron medium could reduce the recombination of photoelectrons and holes, thus leading to the improvement of photocatalytic performance of these catalysts. Due to the unique structure and composite advantages, the optimal Ag2O/AgBr-CeO2 photocatalysts exhibit the superior tetracycline (TC) degradation efficiency of 93.23% and favorable stability with near-initial capacity under visible light irradiation. This ternary Z-scheme structure materials will be the well-promising photocatalysts or the purification of antibiotic wastewater.

GSH-Depleted Nanozymes with Hyperthermia-Enhanced Dual Enzyme-Mimic Activities for Tumor Nanocatalytic Therapy

Nanocatalytic therapy, using artificial nanoscale enzyme mimics (nanozymes), is an emerging technology for therapeutic treatment of various malignant tumors. However, the relatively deficient catalytic activity of nanozymes in the tumor microenvironment (TME) restrains their biomedical applications. Here, a versatile and bacteria-like PEG/Ce-Bi@DMSN nanozyme is developed by coating uniform Bi₂ S₃ nanorods (NRs) with dendritic mesoporous silica (Bi₂ S₃ @DMSN) and then decorating ultrasmall ceria nanozymes into the large mesopores of Bi₂ S₃ @DMSN. The nanozymes exhibit dual enzyme-mimic catalytic activities (peroxidase-mimic and catalase-mimic) under acidic conditions that can regulate the TME, that is, simultaneously elevate oxidative stress and relieve hypoxia. In addition, the nanozymes can effectively consume the overexpressed glutathione (GSH) through redox reaction. Photothermal therapy (PTT) is introduced to synergistically improve the dual enzyme-mimicking catalytic activities and depletion of the overexpressed GSH in the tumors by photonic hyperthermia. This is achieved by taking advantage of the desirable light absorbance in the second near-infrared (NIR-II) window of the PEG/Ce-Bi@DMSN nanozymes. Subsequently the reactive oxygen species (ROS)-mediated therapeutic efficiency is significantly improved. Therefore, this study provides a proof of concept of hyperthermia-augmented multi-enzymatic activities of nanozymes for tumor ablation.

Template Synthesis of Porous Ceria-Based Catalysts for Environmental Application

Porous oxide materials are widely used in environmental catalysis owing to their outstanding properties such as high specific surface area, enhanced mass transport and diffusion, and accessibility of active sites. Oxides of metals with variable oxidation state such as ceria and double oxides based on ceria also provide high oxygen storage capacity which is important in a huge number of oxidation processes. The outstanding progress in the development of hierarchically organized porous oxide catalysts relates to the use of template synthetic methods. Single and mixed oxides with enhanced porous structure can serve both as supports for the catalysts of different nature and active components for catalytic oxidation of volatile organic compounds, soot particles and other environmentally dangerous components of exhaust gases, in hydrocarbons reforming, water gas shift reaction and photocatalytic transformations. This review highlights the recent progress in synthetic strategies using different types of templates (artificial and biological, hard and soft), including combined ones, in the preparation of single and mixed oxide catalysts based on ceria, and provides examples of their application in the main areas of environmental catalysis.

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

Preparation and Luminescence Properties of A-Type Lutecium Silicate Core-Shell Nanospheres

X-ray radio-luminescence materials have potential application in radiotherapy (RT) and biomedical imaging. Considering that lutecium ions (Lu³⁺) with high atomic number (Z) have high X-ray attenuation coefficients, Ce³⁺-doped A-type Lu₂SiO₅@SiO₂ (A-LSO:Ce³⁺@SiO₂) core-shell nanospheres with size in the range of 200-250 nm were prepared through coprecipitation method. The growth mechanism of A-LSO:Ce³⁺@SiO₂ core-shell nanospheres was investigated through determining the phase transition and morphology evolution by XRD, FT-IR, and TEM. The emission spectra, decay profile, and X-ray excited luminescence spectra (XEL) of the obtained samples were collected. The results show that a new type of lutecium silicate core-shell nanospheres A-LSO:Ce³⁺@SiO₂ can be fabricated and exhibit efficient radio-luminescence under X-ray radiation, which has potential application in the diagnosis and therapy of cancer.

Nanoscale Effect of Zirconia Filler Surface on Mechanical Tensile Strength of Polymer Composites

A characteristic effect of a nano-concave-convex structure of a zirconia nanoparticle assembly with an inherent porous structure and huge surface area enabled us to introduce systematic surface modification by thermal treatment to smooth surface and polymer impregnation to mask the nano-concave-convex structure of the zirconia nanoparticle assembly. A polymer composite prepared from 30 wt% poly(N-isopropylacrylamide) containing 0.02 wt% zirconia nanoparticle assembly with the inherent nano-concave-convex surface structure showed the highest tensile strength in mechanical tensile testing. However, both sintered zirconia nanoparticle assembly with smooth surface and zirconia nanoparticle assemblies with polymer masked surface showed lower strength with longer elongation at break in mechanical tensile testing.

Low-Spin-State Hematite with Superior Adsorption of Anionic Contaminations for Water Purification

Hematite attracts intensive interest as an adsorbent for water purification, but the oversized dimension and inherent high-spin Fe(III) restrict its adsorption capability and kinetics. Herein a spatial-confinement strategy is reported that synthesizes ultrafine α-Fe₂ O₃ benefiting from nanogrids constructed by predeposition of TiO₂ nanodots in the MCM-41 channel, and that tunes the spin-state of Fe(III) from high-spin to low-spin induced by the strong guest-host interaction between the ultrafine Fe₂ O₃ with SiO₂ (MCM-41). The low-spin Fe(III) endorses strong bonding with anionic adsorbates, and significantly facilitates the electrons transfer from Fe₂ O₃ to SiO₂ to form a highly positive charged surface, and thereby shows superior electrostatic multilayer adsorption performance to different kinds of anionic contaminations. Specifically, the maximum uptake, adsorption rate, and distribution coefficient (K_d ) for Rose Bengal dye reach as high as 1810 mg g^-1 , 1644 g (g min)^-1 , and 2.2 × 10⁶ L kg^-1 , which are more than 8, 230, and 3700 times higher than those of commercial activated carbon, respectively. It also shows outstanding purification performance for real field water. It is demonstrated that a strong guest-host interaction can alter the spin-state of transition metal oxides, which may pave a new way to improve their performance in adsorption and other applications like catalysis.

Macroscopic Hexagonal Co3O4 Tubes Derived from Controllable Two-Dimensional Metal-Organic Layer Single Crystals: Formation Mechanism and Catalytic Activity

Macroscopic Co₃O₄ hexagonal tubes were successfully synthesized using hollow two-dimensional (2D) MOL (metal-organic layer) single crystals as sacrificial templates. The hollow 2D MOL single crystals were prepared under hydrothermal conditions with acetonitrile (MeCN) as an interference agent. The formation of hollow-structured 2D MOL single crystals was tracked by time-dependent experiments, and two simultaneous paths-namely, the crystal-to-crystal transformation in solution and the dissolution + migration (toward the external surface) of inner crystallites-were identified as playing a key role in the formation of the unique hollow structure. The calculated change in Gibbs free energy (ΔG = -1.18 eV) indicated that the crystal-to-crystal transformation was spontaneous at 393 K. Further addition of MeCN as an interference agent eventually leads to the formation of macroscopic hexagonal tubes. Among all of the as-synthesized Co₃O₄, Co-MeCN-O with a hexagonal tube morphology exhibited the best catalytic performance in toluene oxidation, it achieved a toluene conversion of 90% (T₉₀) at ∼227 °C (a space velocity of 60 000 mL g^-1 h^-1) and the activity energy (E_a) is 69.5 kJ mol^-1. A series of characterizations were performed to investigate the structure-activity correlation. It was found that there are more structure defects, more adsorbed surface oxygen species, more surface Co³⁺ species, and higher reducibility at low temperatures on the Co-MeCN-O than on other Co₃O₄ samples; these factors are responsible for its excellent catalytic performance. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) characterization showed that, when there is no oxygen in the atmosphere, the lattice oxygen may be involved in the activation of toluene, and the gas-phase oxygen replenished by the oxygen vacancies was essential for the total oxidation of toluene on the surface of the Co-MeCN-O catalysts, it also proves the importance of oxygen vacancies. Moreover, for the Co-MeCN-O catalysts, no obvious decrease in catalytic performance was observed after 120 h at 220 °C and it is still stable after cycling tests, which indicates that it exhibits excellent stability for toluene oxidation. This study sheds lights on the controllable synthesis of macroporous-microporous materials in single-crystalline form without an external template, and, thus, it may serve as a reference for future design and synthesis of hollow porous materials with outstanding catalytic performance.

Stability and Sensing Enhancement by Nanocubic CeO2 with {100} Polar Facets on Graphene for NO2 at Room Temperature

Metal oxides with a polar surface interact strongly with polar NO₂ molecules, thus facilitating sensitive detection of NO₂. In this work, the composites comprising graphene and cubic CeO₂ nanoparticles with the {100} polar surface are prepared by a hydrothermal technique, and they exhibit fast response, excellent selectivity, stable recovery, and sensitive detection with a low detection limitation of 1 ppm for NO₂ at room temperature. According to the first-principle calculations, the adsorption energy of NO₂ on the CeO₂{100} polar surface is the most negative corresponding to the strongest interactions between them. The formation energy of oxygen vacancies (O_v) on the {100} polar plane is also negative, and the abundant O_v facilitates the adsorption of NO₂. The internal electric field near the polar surface promotes the charge separation and accelerates the charge exchange between NO₂ and the composites. In addition, graphene promotes electron transfer at the interface and improves the stability of the CeO₂{100} polar surface. The composites of graphene and metal oxides with a polar surface are excellent for NO₂ detection, and the discovery reveals a new sensing strategy.

Engineering well-defined rare earth oxide-based nanostructures for catalyzing C1 chemical reactions

In this review, we summarize the nanostructural engineering and applications of rare earth oxide-based nanomaterials with well-defined compositions, crystal phases and shapes for efficiently catalyzing C1 chemical reactions.

Multishell Hollow Metal/Nitrogen/Carbon Dodecahedrons with Precisely Controlled Architectures and Synergistically Enhanced Catalytic Properties

Multishell hollow nanoarchitectures are one of the most important branches in the nanomaterial field due to their enormous potential in many fields, but synthesizing them in a well-controlled manner remains challenging. Herein, we present a general strategy for the construction of multishell hollow metal/nitrogen/carbon dodecahedrons (metal@NC) with well-defined and precisely controlled architectures. This strategy is based on the pyrolysis of multilayer solid ZIFs prepared by a step-by-step crystal growth approach, which enables precise control over the shell number and composition of the resultant hollow metal@NC. Impressively, our strategy can be further extended to the synthesis of yolk@multishell hollow structures or multishell hollow structures that are assembled by carbon nanotubes. The multishell hollow structures can efficiently facilitate the mass diffusion, which together with the high dispersity and increased surface area are responsible for their significantly enhanced catalytic performances for the selective hydrogenation of biomass-derived furfural to cyclopentanol when compared with their solid and single-shell counterparts. We anticipate that our general strategy would shed light on the rational design and accurate construction of other complex multishell hollow materials for various important yet challenging applications.

Lanthanide-Doped Photoluminescence Hollow Structures: Recent Advances and Applications

Lanthanide-doped nanomaterials have attracted significant attention for their preeminent properties and widespread applications. Due to the unique characteristic, the lanthanide-doped photoluminescence materials with hollow structures may provide advantages including enhanced light harvesting, intensified electric field density, improved luminescent property, and larger drug loading capacity. Herein, the synthesis, properties, and applications of lanthanide-doped photoluminescence hollow structures (LPHSs) are comprehensively reviewed. First, different strategies for the engineered synthesis of LPHSs are described in detail, which contain hard, soft, self-templating methods and other techniques. Thereafter, the relationship between their structure features and photoluminescence properties is discussed. Then, niche applications including biomedicines, bioimaging, therapy, and energy storage/conversion are focused on and superiorities of LPHSs for these applications are particularly highlighted. Finally, keen insights into the challenges and personal prospects for the future development of the LPHSs are provided.