Fe3O4@C@MCM41-guanidine core-shell nanostructures as a powerful and recyclable nanocatalyst with high performance for synthesis of Knoevenagel reaction

In this study, preparation, characterization and catalytic application of a novel core-shell structured magnetic with carbon and mesoporous silica shells supported guanidine (Fe₃O₄@C@MCM41-guanidine) are developed. The Fe₃O₄@C@MCM41-guanidine was prepared via surfactant directed hydrolysis and condensation of tetraethyl orthosilicate around Fe₃O₄@C NPs followed by treatment with guanidinium chloride. This nanocomposite was characterized by using Fourier transform infrared spectroscopy, vibrating sample magnetometry, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, thermal gravimetric analysis, wide-angle X-ray diffraction and low-angle X-ray diffraction techniques. This nanocomposite have high thermal, chemical stability, and uniform size. Fe₃O₄@C@MCM41-guanidine catalyst demonstrated high yield (91-98%) to prepare of Knoevenagel derivatives under the solvent free conditions at room temperature in the shortest time. Also, this catalyst was recovered and reused 10 times without significant decrease in efficiency and stability. Fortunately, an excellent level of yield (98-82%) was observed in the 10 consecutive catalyst cycles.

Boosting visible light photocatalysis in BiOI/BaFe12O19 magnetic heterojunction

Many previous studies have underestimated the role of magnetic components in improving photocatalytic performance. It is significance to explore the migration mechanism of photoinduced carriers in magnetic heterojunction. Here, a magnetic heterojunction, BiOI/BaFe₁₂O₁₉, was synthesized by a simple preparation method. The optimal synthesis conditions and photocatalytic reaction conditions were explored. The growth mechanism of bismuth iodide oxide (BiOI) was elaborated by introducing a micromagnetic field stemming from barium ferrite (BaFe₁₂O₁₉). The electrochemical impedance spectroscopy (EIS), Mott-Schottky curve (MS), transient fluorescence spectrometer (PL), and photocurrent response plot (i ~ t) tests indicated that the BiOI/BaFe₁₂O₁₉ possessed a higher transfer capacity of electrons, higher separation efficiency of photoinduced carriers, stronger photocurrent response, and higher carriers density, compared with pure BiOI. The ultraviolet-visible diffuse reflectance spectrophotometer (UV-vis DRS), electron paramagnetic resonance spectrometer (EPR), MS, and quenching experiments revealed band structure configuration and migration mechanism of photoinduced carriers. The enhancement mechanism of photocatalysis and photocatalytic reaction mechanism was clearly proclaimed in BiOI/BaFe₁₂O₁₉ catalytic system.

Recent developments on bismuth oxyhalides (BiOX; X = Cl, Br, I) based ternary nanocomposite photocatalysts for environmental applications

Photocatalytic treatment of organic pollutants present in wastewater using semiconductor nanomaterials under light irradiation is one of the efficient advanced oxidation processes. Stable metal oxide (e.g. TiO₂) based semiconductor photocatalytic systems have been mainly investigated for this purpose. Nevertheless, their large band gap (~3.2 eV) makes them inefficient in utilization of visible light portion of solar light leading to a lower degradation efficiency. Investigations have focused on the development of visible light responsive bismuth oxyhalides (BiOX; X = Cl, Br, I), one of the potential nanomaterials with unique layered structure, for efficient absorption of solar light for the degradation of pollutants. However, the rapid recombination rate of photogenerated charge carriers limits their practical applicability. To overcome such drawbacks, the development of BiOX based ternary nanocomposites received significant attention because of their unique structural and electronic properties, improved visible light response and increased separation and transfer rate of photogenerated charge carriers. This review aims to provide a comprehensive overview of the recent developments on bismuth oxyhalides-based ternary nanocomposites for enhanced environmental pollutants decomposition under visible light irradiation. The principles of photocatalysis, synthetic methodologies of bismuth oxyhalides and their characteristics such as heterojunctions formation, improved visible light response and separation rate of charge carriers and the mechanisms for enhanced visible light photocatalytic activity are discussed. In addition, the future prospects on the improvement in the photocatalytic activity of bismuth oxyhalides-based ternary nanocomposites are also discussed. This review could be beneficial for designing new ternary nanocomposites with superior visible light photocatalytic efficiency.

Historical development and prospects of photocatalysts for pollutant removal in water

Photocatalysis, as a low-cost and environment friendly technology, has demonstrated a significant potential for water pollution purification; it has received extensive attention in recent decades. The key is the photocatalyst; a large number of photocatalysts have been developed. To better understand and further develop the photocatalysis technology for water treatment, this review summarizes its development over time. The development period is divided into four stages (1960s-1993, 1994-2000, 2001-2010, and 2011-present) to provide readers with a better understanding of the development characteristics, and causes and consequences of each historical stage. This review expounds the origin and development of photocatalysis and the obstacles encountered and overcome. It describes the development of mechanisms and methods to solve these problems in each time period. Moreover, it reviews the recent development of new photocatalysts, the concept of designing photocatalysts, and photocatalytic-coupling systems. Finally, it enumerates the problems that continue to exist in the application of photocatalysis technology, and highlights the key issues that must be addressed in future research. The review is aimed at providing the researchers with a deeper understanding of photocatalysis technology and encourage further development of the application of photocatalysis to water treatment.

Photocatalytic Degradation of Methyl Orange by Magnetically Retrievable Supported Ionic Liquid Phase Photocatalyst

A magnetically retrievable ferrocene appended supported ionic liquid phase (SILP) photocatalyst containing a molybdate anion has been synthesized and characterized by Fourier transform infrared, X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray diffraction, energy dispersive spectroscopy, and vibrating sample magnetometer analysis. The optical properties of the photocatalyst were probed by photoluminescence and UV-vis diffuse reflectance spectroscopy. The discharge of undesirable dye effluents from textile industrial plants in the environment is the major concern of environmental pollution and toxicity. In this context, we employed the as-prepared SILP photocatalyst for degradation of methyl orange (MO) under UV light (365 nm) irradiation, and subsequently, recycling studies were performed. The histological alteration in gills of the fish is employed as a tool for monitoring toxins in the environment. In view of this, the histo-toxicological assessment on freshwater fish Tilapia mossambica gills asserted the damage of secondary gill lamellae due to MO. Conversely, structural modifications in the gill architecture were not observed by virtue of photodegraded products confirming that the degraded product is nontoxic in nature. Additionally, the normal behavior of fishes on exposure to photodegraded products reveals that research findings are beneficial for the aquatic ecosystem.

Magnetically separable BiOBr/Fe3O4@SiO2 for visible-light-driven photocatalytic degradation of ibuprofen: Mechanistic investigation and prototype development

The increasingly ubiquitous release of emerging refractory pollutants into water is a serious concern due to associated risks. In this study, mesoporous hierarchical BiOBr/Fe₃O₄@SiO₂-a solvothermally synthesized visible-light-driven magnetic photocatalyst-not only exhibited fast kinetics (t_1/2 = 8.7 min) in the photocatalytic degradation of ibuprofen in water but also achieved almost complete mineralization over a prolonged irradiation of 6 h. Various reactive species, including O₂¯, OH, and H₂O₂, were detected, while the scavenging experiments revealed that e_CB^--mediated reactions and direct-hole oxidation are the major degradation routes. The magnetically recycled BiOBr/Fe₃O₄@SiO₂ maintained ∼80% of its initial photocatalytic activity even after five consecutive cycles. The typically copresent wastewater constituents, including NOM and anions, inhibited the photocatalytic performance to varying extents, and hence necessitated an increase in the photocatalyst dosage to achieve complete ibuprofen degradation in real sewage. Based on the findings of batch experiments, the process was scaled up by developing a 5 L prototype photocatalytic reactor integrated with an electromagnetic separation unit. The results of prototype photocatalytic experiments were comparable to those of batch experiments, and an electromagnetic separation efficiency of ∼99% was achievable in 5 min.

BiOBr hybrids for organic pollutant removal by the combined treatments of adsorption and photocatalysis

The xSiO₂–BiOBr (x = 0–5) and SN–SiO₂–BiOBr hybrids were synthesized via a facile one step co-precipitation method. To determine the optimal formula, the photocatalytic degradation of C. I. reactive red 2 (X3B) with xSiO₂–BiOBr (x = 0–5) was investigated. Under simulated sunlight irradiation, 4SiO₂–BiOBr exhibited a better photocatalytic efficiency than other materials; 1.77 and 1.51 times higher than conventional nano TiO₂ and pure BiOBr, respectively. To demonstrate the photocatalytic degradation mechanism, the effect of active species on degradation of X3B was carried out, and a possible degradation pathway was proposed. To realize the combined treatments of adsorption and photocatalysis, an inorganic/organic (I/O) SN–SiO₂–BiOBr hybrid was further strategized and synthesized. It showed much better adsorption performance than the SiO₂–BiOBr composite. It could enrich organic pollutants by facile adsorption, and then degrade them to H₂O and CO₂ under natural sunlight irradiation. Notably, this sunlight-driven photocatalysis can be performed in the slurry resulted from the pollutant adsorption. As a result, the proposed combination of adsorption and photocatalysis will provide a novel strategy to greatly facilitate the treatment of organic wastewater.

The xSiO₂–BiOBr (x = 0–5) and SN–SiO₂–BiOBr hybrids were synthesized via a facile one step co-precipitation method.

Fe(III)-based metal-organic framework-derived core-shell nanostructure: Sensitive electrochemical platform for high trace determination of heavy metal ions

A new core-shell nanostructured composite composed of Fe(III)-based metal-organic framework (Fe-MOF) and mesoporous Fe₃O₄@C nanocapsules (denoted as Fe-MOF@mFe₃O₄@mC) was synthesized and developed as a platform for determining trace heavy metal ions in aqueous solution. Herein, the mFe₃O₄@mC nanocapsules were prepared by calcining the hollow Fe₃O₄@C that was obtained using the SiO₂ nanoparticles as the template, followed by composing the Fe-MOF. The Fe-MOF@mFe₃O₄@mC nanocomposite demonstrated excellent electrochemical activity, water stability and high specific surface area, consequently resulting in the strong biobinding with heavy-metal-ion-targeted aptamer strands. Furthermore, by combining the conformational transition interaction, which is caused by the formation of the G-quadruplex between a single-stranded aptamer and high adsorbed amounts of heavy metal ions, the developed aptasensor exhibited a good linear relationship with the logarithm of heavy metal ion (Pb²⁺ and As³⁺) concentration over the broad range from 0.01 to 10.0nM. The detection limits were estimated to be 2.27 and 6.73 pM toward detecting Pb²⁺ and As³⁺, respectively. The proposed aptasensor showed good regenerability, excellent selectivity, and acceptable reproducibility, suggesting promising applications in environment monitoring and biomedical fields.

Ag2O/sodium alginate supramolecular hydrogel as a film photocatalyst for removal of organic dyes in wastewater

As a film photocatalyst, a Ag₂O/sodium alginate supramolecular hydrogel exhibited excellent photocatalytic degradability, great adsorptivity, highly efficient charge separation and reusability.

New sterically hindered tin(iv) siloxane precursors to tinsilicate materials: synthesis, spectral, structural and photocatalytic studies

A series of sterically hindered tin(iv) siloxanes (1–8) were synthesized and characterized. The single-source precursors1and3were well suited for producing tinsilicate materials and it act as a photocatalyst for degradation of methylene blue.