Rational Design of α-Fe2O3/Reduced Graphene Oxide Composites: Rapid Detection and Effective Removal of Organic Pollutants

Porous rod-shaped Fe2O3/Ag/BP: a novel substrate for highly sensitive SERS detection of persistent organic pollutants

A surface enhanced Raman scattering (SERS) substrate of porous rod-shaped ferric oxide (Fe2O3) combined with silver nanoparticles (Ag NPs) and black phosphorus (Fe2O3/Ag/BP) was fabricated to detect the persistent organic pollutants (POPs) at low concentration. The organic pollutant Rhodamine 6G (R6G) was used as the probe molecule to study the performances of Fe2O3/Ag/BP, and 4-chlorobiphenyl (PCB-3) was the target of detection. The limit of detection (LOD) of R6G based on this novel SERS substrate Fe2O3/Ag/BP was as low as 1.0 × 10-15M, which was five orders of magnitude lower than that of Fe2O3/Ag (10-10M). The enhancement factor (EF) of Fe2O3/Ag/BP was 6.44 × 108, which was 3.1 times higher than that of porous rod-shaped Fe2O3/Ag (2.08 × 108). The Raman signal of R6G based on Fe2O3/Ag/BP had a good homogeneity, and the relative standard deviation (RSD) of Raman signal intensities of R6G at 1643 cm-1was only 5.97%. Furthermore, the Fe2O3/Ag/BP substrate exhibited a recyclability through the photocatalytic degradation of R6G. The LOD of PCB-3 based on Fe2O3/Ag/BP was 10-9M. Besides, Fe2O3/Ag/BP had a high SERS activity even it was kept in a centrifuge tube without requiring complicated treatment. These results highlight the potential application of Fe2O3/Ag/BP for ultra-trace detection of POPs in the environment.

Fe2O3/TiO2/reduced graphene oxide-driven recycled visible-photocatalytic Fenton reactions to mineralize organic pollutants in a wide pH range

Photocatalytic Fenton reactions combined the advantages from both photocatalysis and Fenton reaction in mineralizing organic pollutants. The key problems are the efficiency and recycling stability. Herein, we reported a novel Fe2O3/TiO2/reduced graphene oxide (FTG) nanocomposite synthesized by a facile solvothermal method. The TiO2 in FTG degraded organic pollutants and mineralized intermediates via photocatalysis under visible light irradiation, which could also promote Fenton reaction by accelerating Fe3+-Fe2+ recycle. Meanwhile, the Fe2O3 rapidly degraded organic pollutants via Fenton reactions, which also promoted photocatalysis by enhancing visible light absorbance and diminishing photoelectron-hole recombination. The high distribution of TiO2 and Fe2O3 on rGO, together with their strong interaction resulted in enhanced synergetic cooperation between photocatalysis and Fenton reactions, leading to the high mineralization efficiency of organic pollutants. More importantly, it could also inhibit the leaching of Fe species, leading to the long lifetime of FTG during photocatalytic Fenton reactions in a wide pH range from 3.4 to 9.2.

Harvesting visible light for enhanced catalytic degradation of wastewater using TiO2@Fe3O4 embedded on two dimensional reduced graphene oxide nanosheets

Carbon-integrated binary metal oxide semiconductors have gained prominence in the last decade as a better material for photocatalytic wastewater treatment technology. In this regard, this research describes the investigation of the binary metal oxide TiO2@Fe3O4 embedded on reduced graphene oxide (rGO) nanosheets synthesized through a combination of sol-gel, chemical precipitation, and Hummer's processes. Besides, the catalyst is applied for the photocatalytic degradation of organic chlorophenol pollutants. The characterized diffraction results showed the peak broadening of the rGO-TiO2@Fe3O4 composite formed with tetragonal and cubic structures having small crystallite sizes. The TEM observation shows an enormous miniature of TiO2@Fe3O4 nanospheres spread on the folded 2D-rGO nanosheets with a large BET surface area. The XPS result holds the mixed phases of Fe3O4 and Fe2O3. Finally, the catalyst demonstrated a low band gap with extended light absorption towards visible light irradiation. The synergistic interactions between Fe3+ and Fe2+ improved the visible light activity due to the incorporation of rGO, and also possessed good recycling capacity. The increased mobility of electrons at the interfaces of TiO2 and Fe3O4 due to the mixing of rGO results in the separation of charge carriers by elevating the photocatalytic degradation efficiency of chlorophenol.

Graphene oxide:Fe2O3 nanocomposites for photodetector applications: experimental and ab initio density functional theory study

In this report, a GO:Fe2O3 nanocomposite was synthesized using a one-step covalent attachment approach using a sol-gel technique. The optical absorbance, photoconductive, photo-capacitive, and electrical properties were obtained using spectroscopy, and current-voltage (I-V) measurements. An enhanced optical absorbance with corresponding band gap reduction is observed when Fe2O3 nanoparticles are incorporated in GO. A corresponding enhanced photoconductance in the order of ×101 was observed due to the impact of band gap narrowing. The enhanced photoconductivity and photo-capacitance can be attributed to energy and charge transfer between GO and Fe atoms, leading to the generation of photo-induced excitons. Density function theory calculations indicate increased charge transfer when GO is doped with Fe-O atoms, which is consistent with experimental data. The observed results could potentially enable the use of GO:Fe2O3 nanocomposites for photodetectors and other optoelectronic applications.

Graphene oxide-incorporated silver-based photocatalysts for enhanced degradation of organic toxins: a review

Environmental contamination and scarcity of energy have been deepening over the last few decades. Heterogeneous photocatalysis plays a prominent role in environmental remediation. The failure of earlier metal oxide systems like pure TiO₂ and ZnO as stable visible-light photocatalysts demanded more stable catalysts with high photodegradation efficiency. Silver-based semiconductor materials gained popularity as visible-light-responsive photocatalysts with a narrow bandgap. But their large-scale usage in natural water bodies for organic contaminant removal is minimal. The factors like self-photocorrosion and their slight solubility in water have prevented the commercial use. Various efforts have been made to improve their photocatalytic activity. This review focuses on those studies in which silver-based semiconductor materials are integrated with carbonaceous graphene oxide (GO) and reduced graphene oxide (RGO). The decoration of Ag-based semiconductor components on graphene oxide having high-surface area results in binary composites with enhanced visible-light photocatalytic activity and stability. It is found that the introduction of new efficient materials further increases the effectiveness of the system. So binary and ternary composites of GO and Ag-based materials are reviewed in this paper.

Flexible surface-enhanced Raman scatting substrates: recent advances in their principles, design strategies, diversified material selections and applications

Surface-enhanced Raman scattering (SERS) is widely used as a powerful analytical technology in cutting-edge areas such as food safety, biology, chemistry, and medical diagnosis, providing ultra-fast, ultra-sensitive, nondestructive characterization and achieving ultra-high detection sensitivity even down to the single-molecule level. Development of Raman spectroscopy is strongly dependent on high-performance SERS substrates, which have long evolved from the early days of rough metal electrodes to periodic nanopatterned arrays building on solid supporting substrates. For rigid SERS substrates, however, their applications are restricted by sophisticated pretreatments for detecting solid samples with non-planar surfaces. It is therefore essential to reassert the principles in constructing flexible SERS substrates. Herein, we comprehensively review the state-of-the-art in understanding, preparing and using flexible SERS. The basic mechanisms behind the flexible SERS are briefly outlined, typical design strategies are highlighted and diversified selection of materials in preparing flexible SERS substrates are reviewed. Then the recent achievements of various interdisciplinary applications based on flexible SERS substrates are summarized. Finally, the challenges and perspectives for future evolution of flexible SERS and their applications are demonstrated. We propose new research directions focused on stimulating the real potential of SERS as an advanced analytical technique for commercialization.

Fabrication of spherical porous pAg2O-nWO3/Ag/GNS heterostructure with enhanced photocatalytic activity through plasmonic S-scheme mechanism and its complementing biological interest

The synthesis and characterization of Ag₂OWO₃/Ag/GNS heterostructure with desired modifications has been elucidated in the contemporary study. The fabrication involves a simple hydrothermal method for the configuration of fascinating heterostructures intended to photo-catalytically degrade Eosin Yellow (EY) dye. The toxic dye molecules were converted into non-toxic molecular intermediates, also the elimination of heavy metals from industrial wastewater, being trapped in the pores of heterostructure. The pn junction photocatalyst with plasmonic resonance of Ag for abolition of electron and hole coupling, enhances the photo-response where the catalyst abides S-Scheme mechanism. The work functions of active photocatalysts as calculated for Ag₂O is 6.61eV and WO₃ is 6.04eV. Furthermore, the Ag₂OWO₃/Ag/GNS photocatalysts recovery and reuse in several trials without any noticeable loss of photocatalytic activity, complimented the recyclability of the heterostructure. To ensure the safety of the environment on heterostructure being released, toxicity analysis were carried out. These Ag₂OWO₃/Ag/GNS heterostructures had optimistic result on cytotoxicity assay, and on Musmusculus skin melanoma cells (B16-F10), with anti-microbial/fungal properties. Thereby, the contemporary experiment upholds efficient photocatalysis and ropes multiple errands on biological applications.

Hematite nanoparticles decorated nitrogen-doped reduced graphene oxide/graphitic carbon nitride multifunctional heterostructure photocatalyst towards environmental applications

The carcinogenic heavy metals and aromatic organic compounds linger as wastewater pollutants implying great menace to the ecological balance. To solve these environmental pollution problems, the photocatalytic process is an...

α-Fe2O3/graphene oxide powder and thin film nanocomposites as peculiar photocatalysts for dye removal from wastewater

In this study, hematite graphene oxide (αFe₂O₃-GO) powder nanocomposites and thin-film hematite graphene oxide (αFe₂O₃-GO) were synthesized for application in the removal of Rhodamine B (RhB) from textile wastewater. αFe₂O₃-GO nanomaterials were placed onto the FTO substrate to form a thin layer of nanocomposites. Different analysis including XRD, FTIR, Raman spectra, XPS, and FESEM were done to analyze the morphology, structure, and properties of the synthesized composites as well as the chemical interactions of αFe₂O₃ with GO. The photocatalytic performance of two synthesized composites was compared with different concentrations of αFe₂O₃-GO. The results showed that powder nanocomposites are more effective than thin-film composites for the removal of RhB dye. αFe₂O₃-GO-5% powder nanocomposites removed over 64% of dye while thin-film nanocomposites had less removal efficiencies with just under 47% removal rate. The reusability test was done for both materials in which αFe₂O₃-GO-5% powder nanocomposites removed a higher rate of dye (up to 63%) in more cycles (6 cycles).

Effect of RGO-Y2O3 and RGO-Y2O3:Cr3+ nanocomposite sensor for dopamine

The RGO-Y₂O₃ and RGO-Y₂O₃: Cr³⁺ (5 mol %) nanocomposite (NC) synthesized by hydrothermal technique. The structure and morphology of the synthesized NCs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Y₂O₃:Cr³⁺ displays spherical-shaped particles. Conversely, the surface of the RGO displays a wrinkly texture connecting with the existence of flexible and ultrathin graphene sheets. The photoluminescence (PL) emission spectra showed series of sharp peaks at 490, 591, and 687 nm which corresponding to ⁴F_9/2 → ⁶H_15/2, ⁴F_9/2 → ⁶H_13/2, and ⁴F_9/2 → ⁶H_11/2 transitions and lies in the blue, orange, and red region. The prepared NCs were used for the preparation of modified carbon paste electrodes (MCPE) in the electrochemical detection of dopamine (DA) at pH 7.4. Both modified electrodes provide a good current response towards voltammetric detection of DA. Doping is an effective method to improve the conductivity of Y₂O₃:Cr³⁺ and developed a method for the sensor used in analytical applications.

In-situ DRIFT investigation of photocatalytic reduction and oxidation properties of SiO2@α-Fe2O3 core-shell decorated RGO nanocomposite

In this work, SiO₂@α-Fe₂O₃ core-shell decorated RGO nanocomposites were prepared via a simple sol-gel method. The nanocomposites were prepared with different weight percentages (10, 30, and 50 wt %) of the SiO₂@α-Fe₂O₃ core-shell on RGO, and the effects on the structural and optical properties were identified. The photocatalytic reduction and oxidation properties of the nanocomposites in the gas phase were assessed through the reduction of CO₂ and oxidation of ethanol using in-situ diffuse-reflectance infrared fourier transform spectroscopy (DRIFT). The prepared nanocomposite with (30 wt %) of SiO₂@α-Fe₂O₃ showed superior photocatalytic activity for the gas phase reduction of CO₂ and oxidation of ethanol. Enhancement in the activity was also perceived when the light irradiation was coupled with thermal treatment. The DRIFT results for the nanocomposites indicate the active chemical conversion kinetics of the redox catalytic effect in the reduction of CO₂ and oxidation of ethanol. Further, the evaluation of photoelectrochemical CO₂ reduction performance of nanocomposites was acquired by linear sweep voltammetry (LSV), and the results showed a significant improvement in the onset-potential (–0.58 V) for the RGO (30 wt %)-SiO₂@α-Fe₂O₃ nanocomposite.

In situ preparation of a nanocomposite comprising graphene and α-Fe2O3 nanospindles for the photo-degradation of antibiotics under visible light

Preparation of α-Fe₂O₃ nanospindle (NS) decorated graphene sheets for antibiotic degradation.

Nanographene oxide-TiO2 photonic films as plasmon-free substrates for surface-enhanced Raman scattering

The development of nanostructured semiconductors with tailored morphology and electronic properties for surface-enhanced Raman scattering (SERS) has been attracting significant attention as a promising alternative to conventional coinage metal SERS substrates. In this work, functionalized TiO₂ photonic crystals by graphene oxide nanocolloids (nanoGO) are demonstrated as highly sensitive, recyclable, plasmon-free SERS substrates that combine slow-photon amplification effects with the high adsorption capacity and surface reactivity of GO nanosheets. Comparative evaluation of photonic band gap engineered nanoGO-TiO₂ inverse opal films was performed on methylene blue SERS detection under different laser excitations in combination with rigorous theoretical simulations of the photonic band structure. A very low detection limit of 6 × 10^-7 M and an enhancement factor of 5 × 10⁴ along with excellent self-cleaning performance and reusability could be achieved by the interplay of slow-photon effects assisted by interfacial charge transfer between the analyte and the nanoGO-TiO₂ semiconducting substrate. Slow-photon management in combination with judicious engineering of chemical enhancement in photonic nanostructures is accordingly proposed as an advanced approach for the design of efficient dielectric SERS substrates.

Broadband nonlinear absorption properties of two-dimensional hexagonal tellurene nanosheets

Two dimensional (2D) Group-VI Te, tellurene, was successfully exfoliated using a liquid phase exfoliation (LPE) method. The prepared tellurene nanosheets possessed a thickness of 4.3-4.6 nm and the lateral dimension ranged from hundreds of nanometers to several microns. The broadband nonlinear absorption properties were explored for the first time (as we know) using a z-scan method with the laser photon energy in the range of 0.73-2.76 eV, corresponding to the near-infrared-visible waveband. Tellurene nanosheets exhibited excellent broadband saturated absorption and optical limiting behaviors. The low saturable intensity and the large modulation depth for saturated absorption with low energy photon excitation highlight the superiority of the infrared band as a saturable absorber. In addition, with large energy excitation, tellurene manifested an apparent two photon absorption behavior in the visible band, thus it can be used as an optical limiting material. By adopting the mode-locking technique, this high-quality saturable absorber can be applied in all-solid-state or fiber lasers to generate ultra-short and ultra-high peak power laser pulses. Meanwhile, tellurene as an optical limiting material can protect the sensitive optical devices and human eyes. So, our work not only demonstrates that tellurene is a promising broadband nonlinear optical material, but also implies its application prospects in optics.

Recent Advances in 2D Inorganic Nanomaterials for SERS Sensing

Surface-enhanced Raman spectroscopy is a powerful and sensitive analytical tool that has found application in chemical and biomolecule analysis and environmental monitoring. Since its discovery in the early 1970s, a variety of materials ranging from noble metals to nanostructured materials have been employed as surface enhanced Raman scattering (SERS) substrates. In recent years, 2D inorganic materials have found wide use in the development of SERS-based chemical sensors owing to their unique thickness dependent physico-chemical properties with enhanced chemical-based charge-transfer processes. Here, recent advances in the application of various 2D inorganic nanomaterials, including graphene, boron nitride, semiconducting metal oxides, and transition metal chalcogenides, in chemical detection via SERS are presented. The background of the SERS concept, including its basic theory and sensing mechanism, along with the salient features of different nanomaterials used as substrates in SERS, extending from monometallic nanoparticles to nanometal oxides, is comprehensively discussed. The importance of 2D inorganic nanomaterials in SERS enhancement, along with their application toward chemical detection, is explained in detail with suitable examples and illustrations. In conclusion, some guidelines are presented for the development of this promising field in the future.

Applications of magnetic nanoparticles in surface-enhanced Raman scattering (SERS) detection of environmental pollutants

Environmental pollution, a major problem worldwide, poses considerable threat to human health and ecological environment. Efficient and reliable detection technologies, which focus on the appearance of emerging environmental and trace pollutants, are urgently needed. Surface-enhanced Raman scattering (SERS) has become an attractive analytical tool for sensing trace targets in environmental field because of its inherent molecular fingerprint specificity and high sensitivity. In this review, we focused on the recent developments in the integration of magnetic nanoparticles (MNPs) with SERS for facilitating sensitive detection of environmental pollutants. An overview and classification of different types of MNPs for SERS detection were initially provided, enabling us to categorize the huge amount of literature that was available in the interdisciplinary research field of MNPs based SERS technology. Then, the basic working principles and applications of MNPs in SERS detection were presented. Subsequently, the detection technologies integrating MNPs with SERS that eventually were used for the detection of various environmental pollutions were reviewed. Finally, the advantages of MNP-basedSERS detection technology for environmental pollutants were concluded, and the current challenges and future outlook of this technology in practical applications were highlighted. The application of the MNPs-basedSERS techniques for environmental analysis will be significantly advanced with the great progresses of the nanotechnologies, optics, and materials.

Preparation of α-Fe2O3/rGO composites toward supercapacitor applications

Preparation of α-Fe₂O₃/rGO composites for supercapacitor application using in situ synthesis and a mechanical agitation method.

Cube-like Fe3O4@SiO2@Au@Ag magnetic nanoparticles: a highly efficient SERS substrate for detection of pesticide

As a novel SERS nanocomposities, cube-like Fe3O4@SiO2@Au@Ag magnetic nanoparticles have been synthesized for the first time. Cube-like α-Fe2O3 NPs with uniform size can be achieved by optimizing reaction temperature and time. Firstly, the cube-like Fe3O4@SiO2 with good dispersity were achieved by calcining α-Fe2O3@SiO2 NPs in hydrogen atmosphere at 360 °C for 2.5 h, followed by self-assembling PEI shell via sonication. Furthermore, the Au@Ag particles can be densely assembled on the Fe3O4@SiO2 NPs to form the Fe3O4@SiO2@Au@Ag composite structure via strong Ag-N interaction. The obtained nanocomposites exhibit an excellent surface-enhanced Raman (SERS) behavior, reflected from low detection of limit (p-ATP) at 5×10-14 M level. Moreover, these nanocubes are used for detection of thiram and the detection limit can reach up to 5×10-11 M, while the rule of U.S. Environmental Protection Agency specifies that the residue in fruit must be lower than 7 ppm. Hence, the resulting substrate with high SERS activity has great practical potential applications in rapid detection of chemical, biological and environment pollutants with a simple portable Raman instrument at trace level.

Effect of reduced graphene oxide on the structural, optical, adsorption and photocatalytic properties of iron oxide nanoparticles

Effect of reduced graphene oxide on the structural and photocatalytic properties of Fe₂O₃ nanoparticles.

Preparation of polydopamine-coated graphene oxide/Fe3O4 imprinted nanoparticles for selective removal of fluoroquinolone antibiotics in water

Antibiotics in water have recently caused increasing concerns for public health and ecological environments. In this work, we demonstrated polydopamine-coated graphene oxide/Fe₃O₄ (PDA@GO/Fe₃O₄) imprinted nanoparticles coupled with magnetic separation for fast and selective removal of fluoroquinolone antibiotics in water. The nanoparticles were prepared by the self-polymerization of dopamine using sarafloxacin as a template. The imprinted PDA film of 10~20 nm uniformly covered the surface of GO/Fe₃O₄ providing selective binding sites. The nanoparticles showed rapid binding and a large capacity (70.9 mg/g). The adsorption data fitted well the Langmuir and pseudo-second order kinetic equations. The nanoparticles could be easily separated by a magnet following the adsorption and then regenerated by simple washing for repetitive adsorptions. The nanoparticles were successfully used for the removal of fluoroquinolone antibiotics in seawater, with removal efficiencies of more than 95%. The proposed strategy has potentials for efficient removal of antibiotics in environmental water.

Sonochemical synthesis of highly branched flower-like Fe3O4@SiO2@Ag microcomposites and their application as versatile SERS substrates

We report a novel strategy for the synthesis of magnetic-based flower-like silver composite microspheres (Fe₃O₄@SiO₂@Ag microflowers) with a highly branched shell structure through a sonochemical-assisted method. The obtained Fe₃O₄@SiO₂@Ag microflowers possess good dispersity, high magnetic responsiveness, and highly reproducible structures. The size and morphology of the silver petal shell of these microflowers can be easily controlled by varying the experimental parameters. The silver petal provides an effectively large surface area for forming sufficient plasmonic hot spots and capturing target molecules. The microscale magnetic core endows microflowers with superior magnetic nature to enrich targeted analytes and create abundant interparticle hot spots through magnetism-induced aggregation. Hence, Fe₃O₄@SiO₂@Ag microflowers could be a versatile SERS substrate, as verified by the detection of the non-adsorbed R6G molecules and the adsorbed pesticide thiram, with a detection limit as low as 1 × 10^-14 M and 1 × 10^-11 M, respectively. We further demonstrate that aptamer-functionalized microflowers can easily capture S. aureus in tap water and significantly enhance their SERS signal. Moreover, the microflowers can be easily recycled because of the intrinsic magnetism of the Fe₃O₄ cores, which indicate a new route in eliminating the "single-use" problem of traditional SERS substrates. These advantages make the microflowers powerful SERS probes for chemical and biological analyses.