Synthesis of Yolk-Shell Structured Fe3O4@void@CdS Nanoparticles: A General and Effective Structure Design for Photo-Fenton Reaction

Broad Spectral Response FeOOH/BiO2-x Photocatalyst with Efficient Charge Transfer for Enhanced Photo-Fenton Synergistic Catalytic Activity

In this work, to promote the separation of photogenerated carriers, prevent the catalyst from photo-corrosion, and improve the photo-Fenton synergistic degradation of organic pollutants, the coating structure of FeOOH/BiO2-x rich in oxygen vacancies was successfully synthesized by a facile and environmentally friendly two-step process of hydrothermal and chemical deposition. Through a series of degradation activity tests of synthesized materials under different conditions, it was found that FeOOH/BiO2-x demonstrated outstanding organic pollutant degradation activity under visible and near-infrared light when hydrogen peroxide was added. After 90 min of reaction under photo-Fenton conditions, the degradation rate of Methylene Blue by FeOOH/BiO2-x was 87.4%, significantly higher than the degradation efficiency under photocatalysis (60.3%) and Fenton (49.0%) conditions. The apparent rate constants of FeOOH/BiO2-x under photo-Fenton conditions were 2.33 times and 3.32 times higher than photocatalysis and Fenton catalysis, respectively. The amorphous FeOOH was tightly coated on the layered BiO2-x, which significantly increased the specific surface area and the number of active sites of the composites, and facilitated the improvement of the separation efficiency of the photogenerated carriers and the prevention of photo-corrosion of BiO2-x. The analysis of the mechanism of photo-Fenton synergistic degradation clarified that ·OH, h+, and ·O2- are the main active substances involved in the degradation of pollutants. The optimal degradation conditions were the addition of the FeOOH/BiO2-x composite catalyst loaded with 20% Fe at a concentration of 0.5 g/L, the addition of hydrogen peroxide at a concentration of 8 mM, and an initial pH of 4. This outstanding catalytic system offers a fresh approach to the creation and processing of iron-based photo-Fenton catalysts by quickly and efficiently degrading various organic contaminants.

Scalability of advanced oxidation processes (AOPs) in industrial applications: A review

Disinfection and decontamination of water by application of oxidisers is an essential treatment step across numerous industrial sectors including potable supply and industry waste management, however, could be greatly enhanced if operated as advanced oxidation processes (AOPs). AOPs destroy contaminants including pathogens by uniquely harnessing radical chemistry. Despite AOPs offer great practical opportunities, no reviews to date have highlighted the critical AOP virtues that facilitate AOPs' scale up under growing industrial demand. Hence, this review analyses the critical AOP parameters such as oxidant conversion efficiency, batch mode vs continuous-flow systems, location of radical production, radical delivery by advanced micro-/mesoporous structures and AOP process costs to assist the translation of progressing developments of AOPs into their large-scale applications. Additionally, the state of the art is analysed for various AOP inducing radical/oxidiser measurement techniques and their half-lives with a view to identify radicals/oxidisers that are suitable for in-situ production. It is concluded that radicals with short half-lives such as hydroxyl (10-4 μsec) and sulfate (30-40 μsec) need to be produced in-situ via continuous-flow reactors for their effective transport and dosing. Meanwhile, radicals/oxidisers with longer half-lives such as ozone (7-10 min), hydrogen peroxide (stable for several hours), and hypochlorous acid (10 min -17 h) need to be applied through batch reactor systems due to their relatively longer stability during transportation and dosing. Complex and costly synthesis as well as cytotoxicity of many micro-/mesoporous structures limit their use in scaling up AOPs, particularly to immobilising and delivering the short-lived hydroxyl and sulfate radicals to their point of applications. Overall, radical delivery using safe and advanced biocompatible micro-/mesoporous structures, radical conversion efficiency using advanced reactor design and portability of AOPs are priority areas of development for scaling up to industry.

Enhanced photocatalytic degradation of amoxicillin using a spinning disc photocatalytic reactor (SDPR) with a novel Fe3O4@void@CuO/ZnO yolk-shell thin film nanostructure

Antibiotics are resistant compounds with low biological degradation that generally cannot be removed by conventional wastewater treatment processes. The use of yolk-shell nanostructures in spinning disc photocatalytic reactor (SDPR) enhances the removal efficiency due to their high surface-to-volume ratio and increased interaction between catalyst particles and reactants. The purpose of this study is to investigate the SDPR equipped to Fe3O4@void@CuO/ZnO yolk-shell thin film nanostructure (FCZ YS) in the presence of visible light illumination in the photocatalytic degradation of amoxicillin (AMX) from aqueous solutions. Stober, co-precipitation, and self-transformation methods were used for the synthesis of FCZ YS thin film nanostructure and the physical and chemical characteristics of the catalyst were analyzed by XRD, VSM,, EDX, FESEM, TEM, AFM, BET, contact angle (CA), and DRS. Then, the effect of different parameters including pH (3-11), initial concentration of AMX (10-50 mg/L), flow rate (10-25 mL/s) and rotational speed (100-400 rpm) at different times in the photocatalytic degradation of AMX were studied. The obtained results indicated that the highest degradation efficiency of 97.6% and constant reaction rate of AMX were obtained under LED visible light illumination and optimal conditions of pH = 5, initial AMX concentration of 30 mg/L, solution flow rate of 15 mL/s, rotational speed of 300 rpm and illumination time of 80 min. The durability and reusability of the nanostructure were tested, that after 5 runs had a suitable degradation rate. Considering the appropriate efficiency of amoxicillin degradation by FCZ YS nanostructure, the use of Fe3O4@void@CuO/ZnO thin film in SDPR is suggested in water and wastewater treatment processes.

Magnetic nanoparticles and magnetic particle spectroscopy-based bioassays: a 15 year recap

Magnetic nanoparticles (MNPs) have unique physical and chemical properties, such as high surface area to volume ratio and size-related magnetism, which are completely different from their bulk materials. Benefiting from the facile synthesis and chemical modification strategies, MNPs have been widely studied for applications in nanomedicine. Herein, we firstly summarized the designs of MNPs from the perspectives of materials and physicochemical properties tailored for biomedical applications. Magnetic particle spectroscopy (MPS), first reported in 2006, has flourished as an independent platform for many biological and biomedical applications. It has been extensively reported as a versatile platform for a variety of bioassays along with the artificially designed MNPs, where the MNPs serve as magnetic nanoprobes to specifically probe target analytes from fluid samples. In this review, the mechanisms and theories of different MPS platforms realizing volumetric- and surface-based bioassays are discussed. Some representative works of MPS platforms for applications such as disease diagnosis, food safety and plant pathology monitoring, drug screening, thrombus maturity assessments are reviewed. At the end of this review, we commented on the rapid growth and booming of MPS-based bioassays in its first 15 years. We also prospected opportunities and challenges that portable MPS devices face in the rapidly growing demand for fast, inexpensive, and easy-to-use biometric techniques.

Heterogeneous photo-Fenton degradation toward sulfonamide matrix over magnetic Fe3S4 derived from MIL-100(Fe)

Magnetic Fe₃S₄ was facilely derived from MIL-100(Fe) as the precursor and thioacetamide (TAA) as the sulfur source under hydrothermal condition. The as-prepared Fe₃S₄ was adopted as catalyst to promote the photo-Fenton process, in which sulfamethoxazole (SMX) was used as representative pollutant sample to test the oxidative degradation performance of Fe₃S₄. The results showed that Fe₃S₄ exhibited excellent photo-Fenton-like oxidation decomposition performances toward sulfamethoxazole (SMX) under both UV and visible light. A possible degradation mechanism over Fe₃S₄ in the photo-Fenton reaction is put forward based on quenching experiments and electron spin resonance (ESR). About 41% total organic carbon (TOC) removal efficiency of sulfamethoxazole (SMX) over the as-prepared Fe₃S₄ can be accomplished within 40 min. As well, different sulfonamide antibiotics (SAs) like sulfamethoxazole (SMX), sulfisoxazole (SIM) and sulfadiazine (SDZ) were selected to further investigate the oxidative degradation activity of Fe₃S₄ in this photo-Fenton-like reaction system, in which the possible degradation pathways of SMX, SIM and SDZ were put forward based on UHPLC-MS analysis. This work provided a new strategy to prepare magnetic Fe₃S₄ as catalyst for advanced oxidation process, which can be easily separated from the treated water samples to accomplish facile recovery and recyclability.

Engineering an oxygen-vacancy-mediated step-scheme charge carrier dynamic coupling WO3−X/ZnFe2O4 heterojunction for robust photo-Fenton-driven levofloxacin detoxification

Schematic representation of the photo-Fenton degradation of levofloxacin under solar-light illumination.

Photothermal-boosted effect of binary CuFe bimetallic magnetic MOF heterojunction for high-performance photo-Fenton degradation of organic pollutants

Overcoming the relatively low catalytic activity and strict acid pH condition of common photo-Fenton reaction is the key to alleviate the serious global burden caused by common organic pollutants. Herein, a binary homologous bimetallic heterojunction of magnetic CuFe₂O₄@MIL-100(Fe, Cu) metal-organic frameworks (MCuFe MOF) with photothermal-boosted photo-Fenton activity is constructed as an ideal practical photo-Fenton catalyst for the degradation of organic pollutants. Through an in-situ derivation strategy, the formed homologous bimetallic heterojunction with binary redox couples can simultaneously improve the visible light harvesting capacity and expedite the separation and transfer of photogenerated electrons/holes pairs, leading to the continuous and rapid circulation of both Fe^III/Fe^II and Cu^II/Cu^I redox couples. Notably, the heterojunction shows intrinsic photo-thermal conversion effect, which is found to be beneficial to boost the photo-Fenton activity. Impressively, MCuFe MOF shows remarkable catalytic performance towards the degradation of various organic pollutants by comprehensively increasing H₂O₂ decomposition efficiency and decreasing the required dosage of MCuFe MOF (0.05 g L^-1) with a wide pH range (3.0-10.0). As such, a photo-Fenton catalyst consisting of binary homologous bimetallic heterojunction is first disclosed, as well as its photothermal-enhanced effect, which is expected to drive great advance in the degradation of organic pollutants for practical applications.

Synthesis of Template-Free Iron Oxyhydroxide Nanorods for Sunlight-Driven Photo-Fenton Catalysis

Designing a photocatalyst with high efficiency using semiconductor materials emerges as a promising approach for the treatment of wastewater. At the same time, it is very essential to develop nondestructive, green, and sustainable techniques for the degradation of refractory pollutants. Here, we have demonstrated a facile route to prepare iron oxyhydroxide nanorods (β-FeOOH) without employment of any templating agent via a light-driven solution chemistry pathway and explored the as-prepared nanorods as the photo-Fenton catalyst under solar light irradiation. The photocatalytic experiments were performed toward the degradation of the aqueous solution of two different pollutants, namely, methylene blue and rhodamine B dyes. We have illustrated the effect of pH of the solution together with the concentration of H₂O₂ during the degradation process and optimized the solution pH as well as the H₂O₂ concentration. The superb photocatalytic efficiency of β-FeOOH is attributed to the generation of reactive oxygen species in the presence of solar light, and these photo-produced reactive oxygen species assist the degradation process. The excellent photocatalytic efficacy and sustainability of β-FeOOH nanorods along with their effortless synthesis approach point to a cost-effective and environmentally benign pathway in fabricating a highly active photocatalyst for the degradation of organic dyes.

Fe-based Fenton-like catalysts for water treatment: Preparation, characterization and modification

Fenton reaction based on hydroxyl radicals () is effective for environment remediation. Nevertheless, the conventional Fenton reaction has several disadvantages, such as working at acidic pH, producing iron-containing sludge, and the difficulty in catalysts reuse. Fenton-like reaction using solid catalysts rather than Fe²⁺ has received increasing attention. To date, Fe-based catalysts have received increasing attention due to their earth abundance, good biocompatibility, comparatively low toxicity and ready availability, it is necessary to review the current status of Fenton-like catalysts. In this review, the recent advances in Fe-based Fenton-like catalysts were systematically analyzed and summarized. Firstly, the various preparation methods were introduced, including template-free methods (precipitation, sol gel, impregnation, hydrothermal, thermal, and others) and template-based methods (hard-templating method and soft-templating method); then, the characterization techniques for Fe-based catalysts were summarized, such as X-ray diffraction (XRD), Brunauer, Emmett and Teller (BET), SEM (scanning electron microscopy)/TEM (transmission electron microscopy)/HRTEM (high-resolution TEM), FTIR (Fourier transform infrared spectroscopy)/Raman, XPS (X-ray photoelectron spectroscopy), ⁵⁷Fe Mössbauer spectroscopy etc.; thirdly, some important conventional Fe-based catalysts were introduced, including iron oxides and oxyhydroxides, zero-valent iron (ZVI) and iron disulfide and oxychloride; fourthly, the modification strategies of Fe-based catalysts were discussed, such as microstructure controlling, introduction of support materials, construction of core-shell structure and incorporation of new metal-containing component; Finally, concluding remarks were given and the future perspectives for further study were discussed. This review will provide important information to further advance the development and application of Fe-based catalysts for water treatment.

Enhancing iron redox cycling for promoting heterogeneous Fenton performance: A review

Conventional water treatment methods are difficult to remove stubborn pollutants emerging from surface water. Advanced oxidation processes (AOPs) can achieve a higher level of mineralization of stubborn pollutants. In recent years, the Fenton process for the degradation of pollutants as one of the most efficient ways has received more and more attention. While homogeneous catalysis is easy to produce sludge and the catalyst cannot be cycled. In contrast, heterogeneous Fenton-like reaction can get over these drawbacks and be used in a wider range. However, the reduction of Fe (III) to Fe(II) by hydrogen peroxide (H₂O₂) is still the speed limit step when generating reactive oxygen species (ROS) in heterogeneous Fenton system, which restricts the efficiency of the catalyst to degrade pollutants. Based on previous research, this article reviews the strategies to improve the iron redox cycle in heterogeneous Fenton system catalyzed by iron materials. Including introducing semiconductor, the modification with other elements, the application of carbon materials as carriers, the introduction of metal sulfides as co-catalysts, and the direct reduction with reducing substances. In addition, we also pay special attention to the influence of the inherent properties of iron materials on accelerating the iron redox cycle. We look forward that the strategy outlined in this article can provide readers with inspiration for constructing an efficient heterogeneous Fenton system.

A CaO2 @Tannic Acid-FeIII Nanoconjugate for Enhanced Chemodynamic Tumor Therapy

Chemodynamic therapy (CDT) is an effective tumor treatment strategy in which Fe^II reacts with hydrogen peroxide (H₂ O₂ ) in tumor cells to produce highly toxic hydroxyl radical (^. OH) through the Fenton reaction. However, the content of endogenous H₂ O₂ in cells is limited, and the reaction between Fe^III and H₂ O₂ is inefficient, greatly limiting the efficiency of the Fenton reaction and reducing the effectiveness of tumor treatment. Therefore, in this work, we designed and synthesized a new type of nano-system (CaO₂ @TA-Fe^III ) for the enhanced CDT of tumors, in which the polyphenolic compound- tannic acid (TA) and Fe^III formed a TA-Fe nano-coating on the surface of calcium peroxide (CaO₂ ) nanospherical aggregates. When the CaO₂ @TA-Fe^III nanoconjugates reach the tumor site, the CaO₂ contained in the nanoconjugates produces H₂ O₂ after disintegration in tumor cells, and the carried TA rapidly reduces Fe^III to Fe^II , solving the two major shortcomings in CDT of (1) insufficient content of H₂ O₂ in cancer cells, and (2) low catalytic efficiency of the Fenton reaction. Additionally, the ^. OH produced in the Fenton reaction induces oxidative stress for the tumor cells, promoting the occurrence of the "calcium overload" process, and thereby accelerating the death of tumor cells. Experimental results in vitro and in vivo showed that CaO₂ @TA-Fe^III nanoconjugates can effectively kill cancer cells and display an excellent tumor therapeutic effect. We believe that the CaO₂ @TA-Fe^III nanoconjugates are a promising new nano-platform for highly effective tumor treatment.

Visible-Light-Mediated Oxidative Amidation of Aldehydes by Using Magnetic CdS Quantum Dots as a Photocatalyst

A magnetic CdS quantum dot (Fe₃ O₄ /polydopamine (PDA)/CdS) was synthesized through a facile and convenient method from inexpensive starting materials. Characterization of the prepared catalyst was performed by means of FTIR spectroscopy, XRD, SEM, TEM, energy-dispersive X-ray spectroscopy, and vibrating-sample magnetometer techniques. Fe₃ O₄ /PDA/CdS was found to be a highly active photocatalyst for the amidation of aromatic aldehydes by using air as a clean oxidant under mild conditions. The photocatalyst can be recovered by magnetic separation and successfully reused for five cycles without considerable loss of its catalytic activity.

A novel 2D/1D core-shell heterostructures coupling MOF-derived iron oxides with ZnIn2S4 for enhanced photocatalytic activity

1D spindle-like iron oxides with controllable phase were synthesized by using MIL-88A-templated pyrolysis under different atmospheres, thermal annealing in N₂ to obtain Fe₃O₄ and in air to obtain α-Fe₂O₃. Then, 2D/1D core-shell heterostructures (ZnIn₂S₄@Fe₃O₄ and ZnIn₂S₄@α-Fe₂O₃) were constructed by in-situ self-assembly strategy. Characterizations indicated that the 2D ultra-thin ZnIn₂S₄ shell with 0.3 μm was homogeneously coated on the surface of 1D Fe₃O₄/α-Fe₂O₃ core with 1 μm, and ZnIn₂S₄@Fe₃O₄ exhibited higher BET surface area (84.5 m² g^-1) compared with ZnIn₂S₄@α-Fe₂O₃ (17.8 m² g^-1), providing more exposed active sites and larger contact area. The ZnIn₂S₄@Fe₃O₄-5 showed the best photocatalytic activity of RhB degradation as compared to ZnIn₂S₄, Fe₃O₄ and ZnIn₂S₄@α-Fe₂O₃. In addition, the degradation rates of MB, BPA and MO over ZnIn₂S₄@Fe₃O₄ were much higher than that of ZnIn₂S₄@α-Fe₂O₃. The proposed photocatalytic mechanism was also discussed: the Fe₃O₄ as an electron acceptor caused Fe³⁺/Fe²⁺ cycle in ZnIn₂S₄@Fe₃O₄ and ZnIn₂S₄@α-Fe₂O₃ followed the Z-scheme mechanism.

Dendritic Mesoporous Organosilica Nanoparticles: A pH-Triggered Autocatalytic Fenton Reaction System with Self-supplied H2O2 for Generation of High Levels of Reactive Oxygen Species

Dendritic mesoporous silica nanoparticles represent a new biomedical application platform due to their special central radial pore structure for the loading of drugs and functional modification. Herein, we report functionalized dendritic mesoporous organosilica nanoparticles (DMONs), a pH-triggered Fenton reaction generator (TA/Fe@GOD@DMONs), incorporating natural glucose oxidase (GOD) in the DMONs with tannic acid (TA) grafted using Fe³⁺ on the surface, that have been designed and constructed for efficient tumor ablation with self-supplied H₂O₂ and accelerated conversion of Fe³⁺/Fe²⁺ by TA. In view of the deficiency of endogenous H₂O₂, the self-supply through the TA/Fe@GOD@DMONs platform represented a high-yielding source of peroxygen. Furthermore, the production of Fe²⁺ induced by TA greatly improved the efficiency of the Fenton reaction resulting in significant tumor inhibition. This new design represents as novel paradigm for the development of autocatalytic Fenton nanosystems for effective treatment of tumors.

Magnetite-based catalysts for wastewater treatment

The increasing number and concentration of organic pollutants in water stream could become a serious threat in the near future. Magnetite has the potential to degrade pollutants via photocatalysis with a convenient separation process. This study discusses in detail the control size and morphology of magnetite nanoparticles, and their composites with co-precipitation, hydrothermal, sol-gel, and electrochemical route. Further photocatalytic enhancement with the addition of metal and porous support was proposed. This paper also discussed the technology to extend the lifetime of recombination through an in-depth explanation of charge transfer. The possibility to use waste materials as catalyst support was also elucidated. However, magnetite-based photocatalysts still require many improvements to meet commercialization criteria.

Ultra-efficient and stable heterogeneous iron-based Fenton nanocatalysts for degrading organic dyes at neutral pH via a chelating effect under nanoconfinement

An ultra-efficient and stable heterogeneous iron-based Fenton nanocatalyst has been developed for degrading organic dyes at neutral pH via a chelating effect under nanoconfinement.

TiO2/Schwertmannite nanocomposites as superior co-catalysts in heterogeneous photo-Fenton process

The heterogeneous photo-Fenton reaction is an effective technique in combating organic contaminants for both soil and water remediation, and extensive studies have focused on enhancing its efficiency and reducing its costs. In this work, we developed novel photo-Fenton catalysts by simply milling commercially available TiO₂ (P25) with Schwertmannite (Sh), a natural iron-oxyhydroxysulfate nanomineral. We expect that the photo-generated electrons from TiO₂ could continuously migrate to Sh, which then could enhance the separation of electron-hole pairs on TiO₂ and accelerate the reduction of Fe(III) to Fe(II) on Sh, leading to high degradation efficiency of the target organic contaminants. SEM and TEM results showed the distribution of TiO₂ on Sh surface for the nanocomposites (TiO₂/Sh). Under simulated sunlight irradiation, the much higher content of Fe(II) was determined on TiO₂/Sh than on Sh via a common method in the iron ore, and the consumption of H₂O₂ and the production of •OH were more significant in the TiO₂/Sh system than those in the TiO₂ and Sh systems. These results well support our hypothesis that the photo-generated electrons could migrate from TiO₂ to Sh on the composites, and can also explain the much higher degradation efficiency of Rhodamine B (RhB) in the TiO₂/Sh system. Besides, TiO₂/Sh had lower Fe dissolution as compared with Sh, and retained high catalytic stability after four repeated cycles. Above merits of the TiO₂/Sh composites, in combining with their simple synthesis method and low-cost property, indicated that they should have promising applications as heterogeneous photo-Fenton catalysts.

Controlled formation of magnetic yolk-shell structures with enhanced catalytic activity for removal of acetaminophen in a heterogeneous fenton-like system

Encapsulating magnetic nanoparticles in a silica shell is a promising approach in many research fields. We recently demonstrated that the magnetic yolk-shell structure of Fe₃O₄@SiO₂, which consists of an inner magnetite core and outer silica shell separated by a hollow void space, and its modified counterparts can be used as an effective catalyst for removal of acetaminophen in a heterogeneous Fenton-like reaction. The present study develops this approach further in an effort to design an effective procedure for preparing an optimum yolk-shell structure capable of greater catalytic performance. We investigated the use of a controlled synthesis strategy to fabricate an Fe₃O₄@SiO₂ yolk-shell structure under varying conditions. Our focus was a single-step process that examines the effects of Stöber solution temperature, tetraethyl orthosilicate (TEOS) and hexadecyltrimethylammonium bromide (CTAB) concentrations, ethanol and water volume ratio, incubation time, and temperature on Fe₃O₄@SiO₂ textural morphologies. The catalytic performance of the prepared materials was evaluated through oxidative degradation of acetaminophen in a heterogeneous Fenton-like reaction. Field emission transmission electron microscopy observation showed that magnetic yolk-shell structures with appropriate diameter, shell thickness, and hollow void space could be generated through tight control of synthesis conditions. Particle size and hollow void space increased when TEOS concentration increased from 22.10 to 88.50 mM. Hollow void space also increased as incubation time increased from 24 h to 72 h or incubation temperature increased from 50 to 90 °C. However, a yolk-shell structure did not form at a TEOS concentration of 11.10 mM, an incubation time of 3 h, or with an inappropriate ratio of ethyl alcohol and deionized water. Catalytic activity for degradation of acetaminophen increased with increasing hollow void space and thinning silica shell. In addition, the selected appropriate materials exhibited effective catalytic performance over five cycles of regeneration. This study demonstrates the significance of controlling the formation of yolk-shell structures, which enabled us to produce Fe₃O₄@SiO₂ yolk-shell structures of desired and predictable size, hollow void space volume, and shell thickness for higher catalytic performance in degradation of pharmaceuticals in heterogeneous Fenton-like systems.

Intratumoral fate of functional nanoparticles in response to microenvironment factor: Implications on cancer diagnosis and therapy

The extraordinary growth and progression of tumor require enormous nutrient and energy. Unregulated behaviors of cancer cell progressing and persistently change of tumor microenvironment (TME) which acts as the soil for cancer growth and metastasis are the ubiquitous features. The tumor microenvironment exhibits some unique features which differ with the normal tissues. While the nanoparticles get through the blood vessel leakage, they encounter immediately and interact directly with these microenvironment factors. These factors may inhibit the diffusion of nanoparticles from penetrating through the tumor, or induce the dissociation of nanoparticles. Different nanoparticles encountered with different intratumoral microenvironment factors end up in different way. Therefore, in this review, we first briefly introduced the formations, distributions, features of some intratumoral microenvironment, and their effects on the tumor progression. They include extracellular matrix (ECM), matrix metalloproteinases (MMPs), acidic/hypoxia environment, redox environment, and tumor associated macrophages (TAMs). We then exemplified how these factors interact with nanoparticles and emphasized the potentials and challenges of nanoparticle-based strategies facing in enhancing intratumoral penetration and tumor microenvironment remodeling. We hope to give a simple understanding of the interaction between these microenvironment factors and the nanoparticles, thus, favors the designing and constructing of more ideal functional nanoparticles.

FeOCl/POM Heterojunctions with Excellent Fenton Catalytic Performance via Different Mechanisms

To enhance the Fenton catalytic performance in a neutral solution under indoor sunlight, a novel FeOCl/polyoxometalate (POM) (FeOCl/POM-W and FeOCl/POM-Mo) composite was successfully synthesized for the first time, which shows significantly improved Fenton catalytic activity and stability for phenol degradation compared with FeOCl. Furthermore, the degradation constants ( k) of FeOCl/POM-Mo (0.08 min^-1) and FeOCl/POM-W (0.06 min^-1) are a factor of 4 and 3 times greater than that of FeOCl (0.02 min^-1), respectively. The enhanced catalytic activity is attributed to the formation of FeOCl/POM heterojunctions, which results in efficient separation of photoinduced electron-hole pairs and electron transfer from POM to FeOCl. Density functional theory calculations indicate a strong interface interaction of Fe-O-Mo and Fe-O-W in the FeOCl/POM heterojunctions. A Z-scheme mechanism for FeOCl/POM-Mo and a double-transfer mechanism for FeOCl/POM-W are proposed for the enhanced catalytic performance. This study sheds new light on the design and fabrication of high-performance photo-Fenton catalysts to overcome the environmental crisis.

Application of pea-like yolk–shell structured Fe3O4@TiO2 nanosheets for photocatalytic and photo-Fenton oxidation of bisphenol-A

Uniform pea-like yolk–shell (PLYS) structured magnetic TiO₂(PLYS-Fe₃O₄@TiO₂) nanosheets have been prepared via a combined kinetics-controlled mechanical force-driven and hydrothermal etching assisted crystallization method and characterized.

Ce3+ self-doped CeOx/FeOCl: an efficient Fenton catalyst for phenol degradation under mild conditions

Herein, a novel Ce³⁺ self-doped CeO_x/FeOCl composite was successfully prepared by a facile method for the first time, which showed remarkable catalytic activity as a Fenton catalyst in the degradation of phenol under the conditions of a neutral solution, room temperature and natural light.

An Adenosine Triphosphate-Responsive Autocatalytic Fenton Nanoparticle for Tumor Ablation with Self-Supplied H2O2 and Acceleration of Fe(III)/Fe(II) Conversion

Chemodynamic therapy (CDT) can efficiently destroy tumor cells via Fenton reaction in the presence of H₂O₂ and a robust catalyst. However, it has faced severe challenges including the limited amounts of H₂O₂ and inefficiency of catalysts. Here, an adenosine triphosphate (ATP)-responsive autocatalytic Fenton nanosystem (GOx@ZIF@MPN), incorporated with glucose oxidase (GOx) in zeolitic imidazolate framework (ZIF) and then coated with metal polyphenol network (MPN), was designed and synthesized for tumor ablation with self-supplied H₂O₂ and TA-mediated acceleration of Fe(III)/Fe(II) conversion. In the ATP-overexpressed tumor cells, the outer shell MPN of GOx@ZIF@MPN was degraded into Fe(III) and tannic acid (TA) and the internal GOx was exposed. Then, GOx reacted with the endogenous glucose to produce plenty of H₂O₂, and TA reduced Fe(III) to Fe(II), which is a much more vigorous catalyst for the Fenton reaction. Subsequently, self-produced H₂O₂ was catalyzed by Fe(II) to generate highly toxic hydroxyl radical (•OH) and Fe(III). The produced Fe(III) with low catalytic activity was quickly reduced to reactive Fe(II) mediated by TA, forming an accelerated Fe(III)/Fe(II) conversion to guarantee efficient Fenton reaction-mediated CDT. This autocatalytic Fenton nanosystem might provide a good paradigm for effective tumor treatment.

Magnetically Recyclable Fe3O4@Zn xCd1- xS Core-Shell Microspheres for Visible Light-Mediated Photocatalysis

Magnetically recyclable photocatalyst has drawn considerable research interest because of its importance in practical applications. Herein, we demonstrate a facile hydrothermal process to fabricate magnetic core-shell microspheres of Fe₃O₄@Zn _xCd_{1- x}S, successfully using Fe₃O₄@ZnS core-shell microspheres as sacrificed templates. The as-prepared magnetically recyclable photocatalysts show efficient photochemical reduction of Cr(VI) under irradiation of visible light. The photochemical reduction mechanism has been studied to illustrate the reduction-oxidation ability of the photogenerated electrons (e^-) and holes (h⁺), which play an important role in the reduction of Cr(VI) to Cr(III) and oxidation of organic dyes. The as-prepared Fe₃O₄@Zn_0.55Cd_0.45S core-shell microspheres show good chemical stability and only a slight decrease in the photocatalytic activity after four recycles. In particular, the as-prepared photocatalysts could be easily recycled and reused by an external magnetic field. Therefore, this work would provide a facile chemical approach for controlled synthesis of magnetic nanostructures combined with alloyed semiconductor photocatalysts for wastewater treatment.

Generalized Synthesis of Ternary Sulfide Hollow Structures with Enhanced Photocatalytic Performance for Degradation and Hydrogen Evolution

A series of ternary sulfide hollow structures have been successfully prepared by a facile glutathione (GSH)-assisted one-step hydrothermal route, where GSH acts as the source of sulfur and bubble template. We demonstrate the feasibility and versatility of this in situ gas-bubble template strategy by the fabrication of novel hollow structures of MIn₂S₄ (M = Cd, Zn, Ca, Mg, and Mn). Interestingly, with the reaction time varying, the hierarchical CdIn₂S₄ microspheres with controlled internal structures can be regulated from yolk-shell, smaller yolk-shell (yolk-shell with shrunk yolk), hollow, to solid. Under visible-light irradiation, all of our prepared CdIn₂S₄ samples with different morphologies were photoactivated. In virtue of the appealing hierarchical hollow structure, the yolk-shell-structured CdIn₂S₄ microspheres exhibited the optimal photocatalytic activity and excellent durability for both the X₃B degradation and H₂ evolution, which can be ascribed to the synergy-promoting effect of the small crystallite size together with the unique structural advantages of the yolk-shell structure. Thus, we hypothesize that this proof-of-concept strategy paves an example of rational design of hollow structured ternary or multinary sulfides with superior photochemical performance, holding great potential for future multifunctional applications.

2D/2D FeOCl/graphite oxide heterojunction with enhanced catalytic performance as a photo-Fenton catalyst

A novel 2D/2D FeOCl/graphite oxide heterojunction has been successfully prepared for the first time and shows remarkable enhanced photo-Fenton catalytic activity and stability.

Nonsacrificial Template Synthesis of Magnetic-Based Yolk-Shell Nanostructures for the Removal of Acetaminophen in Fenton-like Systems

Recently, yolk-shell structured materials with active metal cores have received considerable attention in heterogeneous Fenton-like systems, which have excellent catalytic performance. In this study, we initially attempted the nonsacrificial template synthesis of yolk-shell structured nanoparticles with magnetite cores encapsulated in a mesoporous silica shell (Fe₃O₄@SiO₂) via a modified sol-gel process and then evaluated their catalytic activity for acetaminophen degradation in Fenton-like systems. Second, copper nanoparticles were decorated on the surface of the Fe₃O₄@SiO₂ microspheres (Fe₃O₄@SiO₂@Cu) to enhance the catalytic activity. The morphological, structural, and physicochemical properties of the prepared materials were characterized via X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, field emission transmission electron microscopy, nitrogen adsorption-desorption isotherms, specific surface area, ζ-potential, magnetic properties, and Fourier transform infrared spectroscopy. The results demonstrated a successful fabrication of the targeted materials. The yolk-shell structured materials possess a spherical morphology with an active core, protective shell, and hollow void. The Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂@Cu variants showed acetaminophen removal rates significantly higher compared to those of their counterparts, i.e., the Fe₃O₄ and Fe₃O₄@Cu core-shell structures. Fe₃O₄@SiO₂@Cu showed that the copper nanoparticles were firmly immobilized on the mesoporous silica shell, dramatically improving the catalytic performance. Both the yolk-shell structured Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂@Cu exhibited good separation and satisfactory regeneration properties, which could be recycled six times without any obvious decline in catalytic activity. Overall, the results of this study suggested that Fe₃O₄@SiO₂ and Fe₃O₄@SiO₂@Cu yolk-shell nanostructures could be promising catalysts for a heterogeneous Fenton-like system by which the removal of emerging contaminants can be greatly improved.

Mesocrystalline Zn-Doped Fe3O4 Hollow Submicrospheres: Formation Mechanism and Enhanced Photo-Fenton Catalytic Performance

Uniform and magnetic recyclable mesocrystalline Zn-doped Fe₃O₄ hollow submicrospheres (HSMSs) were successfully synthesized via a simple one-pot solvothermal route and were used for efficient heterogeneous photo-Fenton catalyst. XRD, XPS, Raman spectroscopy, Mössbauer spectroscopy, SEM, HRTEM, and EDX analyses revealed that the shell of HSMSs is highly porous and assembled by oriented attachment of magnetite nanocrystal building blocks with Zn-rich surfaces. Furthermore, a possible formation mechanism of mesocrystalline hollow materials was proposed. First, Fe₃O₄ mesocrystals were assembled by oriented nanocrystals, and a Zn-rich amorphous shell grew on the surfaces. Then, Zn gradually diffused into Fe₃O₄ crystals to form Zn-doped Fe₃O₄ due to the Kirkendall effect with increasing the reaction time. Meanwhile, the inner nanocrystals would be dissolved, and outer particles would grow larger owing to the Ostwald ripening process, leading to the formation of a hollow structure with porous shell. The Zn-doped Fe₃O₄ HSMSs exhibited high and stable photo-Fenton activity for degradation of rhodamine B (RhB) and cephalexin under visible-light irradiation in the presence of H₂O₂, which results from their hollow mesocrystal structure and Zn doping. It could be easily separated and reused by an external magnetic field. The results suggested that the as-obtained magnetite hollow mesocrystals could be a promising catalyst in the photo-Fenton process.

Facile synthesis of FeOCl/iron hydroxide hybrid nanosheets: enhanced catalytic activity as a Fenton-like catalyst

A facile rapid thermal annealing method to prepare FeOCl/iron hydroxide hybrid nanosheets is reported.

In situ synthesis and immobilization of a Cu(ii)–pyridyl complex on silica microspheres as a novel Fenton-like catalyst for RhB degradation at near-neutral pH

A Cu(ii)–pyridyl complex was in situ synthesized and immobilized onto silica microspheres as a highly effective Fenton-like catalyst at near-neutral pH.

VUV/UV light inducing accelerated phenol degradation with a low electric input

This study presents the first evidence for the accelerated degradation of phenol by Fenton's reagent in a mini-fluidic VUV/UV photoreaction system (MVPS). A low-pressure mercury lamp used in the MVPS led to a complete degradation of phenol within 4-6 min. The HO˙ and HO₂˙ originating from both Fenton's reagent and VUV photolysis of water were identified with suitable radical scavengers. The effects of initial concentrations of phenol, H₂O₂ and Fe³⁺ as well as solution pH on phenol degradation kinetics were examined. Increasing the initial phenol concentration slowed down the phenol degradation, whereas increasing the initial H₂O₂ or Fe³⁺ concentration accelerated the phenol degradation. The optimal solution pH was 3.7. At both 254 and 185 nm, increasing phenol concentration enhanced its absorption for the incident photons. The reaction mechanism for the degradation of phenol was suggested consistent with the results obtained. This study indicates that the VUV/UV photo-Fenton process has potential applications in the treatment of industrial wastewater containing phenol and related aromatic pollutants.

Ultra-sustainable Fe78Si9B13 metallic glass as a catalyst for activation of persulfate on methylene blue degradation under UV-Vis light

Stability and reusability are important characteristics of advanced catalysts for wastewater treatment. In this work, for the first time, sulfate radicals (SO4∙-) with a high oxidative potential (Eo = 2.5-3.1 V) were successfully activated from persulfate by a Fe78Si9B13 metallic glass. This alloy exhibited a superior surface stability and reusability while activating persulfate as indicated by it being used for 30 times while maintaining an acceptable methylene blue (MB) degradation rate. The produced SiO2 layer on the ribbon surface expanded strongly from the fresh use to the 20th use, providing stable protection of the buried Fe. MB degradation and kinetic study revealed 100% of the dye degradation with a kinetic rate k = 0.640 within 20 min under rational parameter control. The dominant reactive species for dye molecule decomposition in the first 10 min of the reaction was hydroxyl radicals (∙OH, Eo = 2.7 V) and in the last 10 min was sulfate radicals (SO4∙-), respectively. Empirical operating variables for dye degradation in this work were under catalyst dosage 0.5 g/L, light irradiation 7.7 μW/cm2, and persulfate concentration 1.0 mmol/L. The amorphous Fe78Si9B13 alloy in this work will open a new gate for wastewater remediation.