Silica Matrix Research Articles

Encapsulated Colorimetric Indicators used as Additives During the Polymerization of Smart Polyethylene

AbstractA number of colorimetric pH indicators (phenolphthalein, bromocresol green, 4‐nitrophenol, phenol red, and bromothymol blue) are encapsulated within silica particles via an acid‐catalyzed sol–gel process. The fabricated indicator is added during ethylene polymerization with a metallocene (Cp2ZrCl2) catalyst. Introduction of the indicator into the silica matrix affects the surface area, probably by partially blocking some of the pores. The encapsulated pH indicator reduces the catalytic activity by up to 17%, whereas adding a solution of the indicator reduced the catalytic activity by up to 34%. The crystallinities of the samples containing the silica‐encapsulated pH indicators are lower than those of the samples to which the pH indicator is added in solution form. The prepared encapsulated colorimetric pH indicators are analyzed by diffuse reflectance UV‐vis spectroscopy. The measured color values are distributed according to the CIE Lab lightness psychometric color space. Addition of the indicator in solution form (free) to the ethylene polymerization reaction does not result in indicator activity in acidic or alkaline media. The pH indicators incorporated into the polyethylene show color changes when exposed to acidic and alkaline media. Samples to which the unencapsulated pH indicators (free) are added exhibit lower catalytic activities and higher crystallinities than the samples containing the encapsulated pH.

Green Chemistry for the Transformation of Chlorinated Wastes: Catalytic Hydrodechlorination on Pd-Ni and Pd-Fe Bimetallic Catalysts Supported on SiO2

Monometallic catalysts based on Fe, Ni and Pd, as well as bimetallic catalysts based on Fe-Pd and based on Ni-Pd supported on silica, were synthesized using a sol-gel cogelation process. These catalysts were tested in chlorobenzene hydrodechlorination at low conversion to consider a differential reactor. In all samples, the cogelation method allowed very small metallic nanoparticles of 2-3 nm to be dispersed inside the silica matrix. Nevertheless, the presence of some large particles of pure Pd was noted. The catalysts had specific surface areas between 100 and 400 m2/g. In view of the catalytic results obtained, the Pd-Ni catalysts are less active than the monometallic Pd catalyst (<6% of conversion) except for catalysts with a low proportion of Ni (9% of conversion) and for reaction temperatures above 240 °C. In this series of catalysts, increasing the Ni content increases the activity but leads to an amplification of the catalyst deactivation phenomenon compared to Pd alone. On the other hand, Pd-Fe catalysts are more active with a double conversion value compared to a Pd monometallic catalyst (13% vs. 6%). The difference in the results obtained for each of the catalysts in the Pd-Fe series could be explained by the greater presence of the Fe-Pd alloy in the catalyst. Fe would have a cooperative effect when associated with Pd. Although Fe is inactive alone for chlorobenzene hydrodechlorination, when Fe is coupled to another metal from the group VIIIb, such as Pd, it allows the phenomenon of Pd poisoning by HCl to be reduced.

Development of date seed extract encapsulated MCM-41: Characterization, release kinetics, antioxidant and antibacterial studies

The encapsulation of natural bioactive compounds in porous support can lead to a sustained release of antioxidants and antimicrobial substances. In this study, the natural antioxidant of date seed extract (DSE) was encapsulated into the mesoporous silica matrix (MCM-41) through the physical vacuum impregnation method. Various characterization studies confirmed the successful encapsulation of DSE into MCM-41 with an encapsulation efficiency of 91%. Date seed extract encapsulated MCM-41(DSE@MCM-41) exhibited rougher morphology, lower specific surface area (1.2 m2 g−1), and lower pore volume (0.023 g cm−3) than MCM-41, indicating higher loading of DSE into the MCM-41 pore channels. The in vitro release profile and bioactive DSE@MCM-41 release kinetics were determined using phosphate buffer solution at pH 5.2 and 7.4. Studies showed that DSE release from DSE@MCM-41 followed first-order kinetics with a sustained release rate, preferably in an acidic medium. The results of radical scavenging activity also showed that the release of antioxidants from DSE@MCM-41 was more sustained than that of free DSE when stored at 4 °C for 3 months. Furthermore, antibacterial studies of DSE@MCM-41 against Escherichia coli and Staphylococcus aureus showed a significant and sustained bactericidal effect at a concentration of 10 mg/mL. These results suggest that DSE-encapsulated MCM-41 could be used as a sustainable-release nanocarrier to extend the shelf-life of food in food packaging applications.

Synthesis of porous, hydrophobic aerogel through the reinforcement of bamboo-shaped oxidized multi-walled carbon nanotubes in the silica matrix for oil spill cleaning

Synthesis of porous, hydrophobic aerogel through the reinforcement of bamboo-shaped oxidized multi-walled carbon nanotubes in the silica matrix for oil spill cleaning

Research on synthesis and nucleation mechanism of silicon nanowire by silver catalysis in molten salt

Molten salt electrolytic synthesis of silicon is identified as a potential industry method due to its thorough deoxidization of oxide and short-flow synthetic progress. However, figuring out a more efficient and sustainable strategy for the increase of the reduction process as well as the control of product morphology still needs endless research. In this study, benefiting from the high electrical conductivity of metallic silver and the easy separation of silver from silver-silicon alloys during the electrolysis of SiO2, metallic silver was introduced to electric-catalyze the production of silicon. Firstly, metallic silver was introduced into the silica matrix by a simple silver mirror reaction. Secondly, the mixed Ag\\SiO2 precursor was located at the cathode for molten salt electrolysis. Finally, silicon nanowires were herein achieved in molten NaCl–CaCl2. Mechanisms of metal Ag played during the electric-polarization process of silica and the electrochemical nucleation of silicon were further analyzed by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Field-Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Raman spectra. The results demonstrate that Ag helps construct Si nanowires via a classic Ag-Si binary alloy-droplet process and provided quantitative guidance for the large-yield production of silicon nanowires via adding 0.08–0.17 g Ag versus 1 g SiO2, controlling the temperature at 850–900 °C and electrolysis voltage at 2.6–2.8 V (2.6V at first 1 h and 2.8V at last 5 h). The synthesized silicon nanowires present two types of linear structures based on two three-phase interlines (3PIs) models and a streamed long-straight nanowire is observed.

Spatially Formed Tenacious Nickel-Supported Bimetallic Catalysts for CO2 Methanation under Conventional and Induction Heating

The paper introduces spatially stable Ni-supported bimetallic catalysts for CO2 methanation. The catalysts are a combination of sintered nickel mesh or wool fibers and nanometal particles, such as Au, Pd, Re, or Ru. The preparation involves the nickel wool or mesh forming and sintering into a stable shape and then impregnating them with metal nanoparticles generated by a silica matrix digestion method. This procedure can be scaled up for commercial use. The catalyst candidates were analyzed using SEM, XRD, and EDXRF and tested in a fixed-bed flow reactor. The best results were obtained with the Ru/Ni-wool combination, which yields nearly 100% conversion at 248 °C, with the onset of reaction at 186 °C. When we tested this catalyst under inductive heating, the highest conversion was observed already at 194 °C.

Enhanced Skin Penetration of Cannabidiol Using Organosilane Particles as Transdermal Delivery Vehicles.

There is potential for cannabidiol to act as an analgesic, anxiolytic and antipsychotic active ingredient; however, there is a need to find alternate administration routes to overcome its low oral bioavailability. In this work, we propose a new delivery vehicle based on encapsulation of cannabidiol within organosilica particles as drug delivery vehicles, which are subsequently incorporated within polyvinyl alcohol films. We investigated the long-term stability of the encapsulated cannabidiol, as well as its release rate, in a range of simulated fluids with different characterization techniques, including Fourier Transform Infrared (FT-IR) and High-performance Liquid Chromatography (HPLC). Finally, we determined the transdermal penetration in an ex vivo skin model. Our results show that cannabidiol is stable for up to 14 weeks within polyvinyl alcohol films at a range of temperatures and humidity. Release profiles are first-order, consistent with a mechanism involving diffusion of the cannabidiol (CBD) out of the silica matrix. The silica particles do not penetrate beyond the stratum corneum in the skin. However, cannabidiol penetration is enhanced and is detected in the lower epidermis, which was 0.41% of the total CBD in a PVA formulation compared with 0.27% for pure CBD. This is partly due to an improvement of its solubility profile as it is released from the silica particles, but we cannot rule out effects of the polyvinyl alcohol. Our design opens a route for new membrane technologies for cannabidiol and other cannabinoid products, where administration via non-oral or pulmonary routes can lead to better outcomes for patient cohorts in a range of therapeutics.

Heavily Doped Si Nanocrystals Formed in P-(SiO/SiO2) Multilayers: A Promising Route for Si-Based Infrared Plasmonics

As building blocks of multifunctional materials involving coupling at the nanoscale, highly doped semiconductor nanocrystals are of great interest for potential applications in nanophotonics. In this work, we investigate the plasmonic properties of highly doped Si nanocrystals embedded in a silica matrix. These materials are obtained by evaporation of heavily phosphorus-doped SiO/SiO2 multilayers in an ultrahigh vacuum chamber followed by rapid thermal annealing. For P contents between 0.7 and 1.9 atom %, structural investigations at the nanoscale give clear evidence that P atoms are mainly located in the core of Si nanocrystals with concentrations reaching up to 10 atom %, i.e., well beyond the solid solubility limit of P in bulk Si. Alloying and formation of SiP nanoparticles are observed for P contents exceeding 4 atom % in the multilayer. Infrared absorption measurements give evidence of a localized surface plasmon resonance located in the 3–6 μm range. A core–shell structure was used to model Si nanocrystals embedded in a silica matrix. Based on the Mie theory and the Drude model, both the mobility and the free charge carrier density were extracted from the simulation, with values reaching 27 cm2 V–1 s–1 and 2.3 × 1020 cm–3, respectively. This results in a dopant activation rate of about 8%.

Using Confocal Laser Scanning Microscopy to Analyze the Mass Transfer in the Protein A Medium of a Silica Matrix

Mass transfer in a protein A medium with a silica matrix was analyzed in this study. Using confocal laser scanning microscopy, we monitored the positional and temporal changes in the polyclonal human IgG during batch adsorption. A simple theoretical model based on Fick’s law of diffusion and Langmuir adsorption was used to numerically approximate the external and intraparticle mass-transfer properties of IgG in single particles. The diffusivities found in this study were validated by comparing with the values reported in other studies and also by using numerical calculation to reproduce the experimentally obtained breakthrough curve.

Preliminary Study of Modified Fluorescent Silica Nanoparticles for the Detection of IgY Antibody

Biosensors must display high sensitivity and selectivity with fast response and be cost-effective. Silica nanoparticles are profoundly promising as versatile signal platforms opening up new possibilities for bioassays and dynamic units in biosensing systems. Fluorescent silica nanoparticles (FSNP) may be a key nanomaterial for labeling antibodies or antigens for biosensor application. Integration FSNP with functional molecules utilizing different surface modification techniques can bring out great improvements such as selective recognition, sensitive detection, and signal amplification because FSNP can bind with a large number of dye molecules within a silica matrix. The FSNP conjugated with anti-IgY can be applied for the detection of IgY antibody. FSNP was fabricated using the sol-gel method with hydrosilylation techniques for silica surface modification. N-H of amide groups from FSNP-anti-IgY ware observed in the FTIR spectra at 1648 cm-1 indicating that the conjugation was successful. The fluorescence intensity of FSNP-anti-IgY after detection of IgY was applied for immunodetection and measured using fluorescence spectroscopy. The intensity of FSNP-anti-IgY was 156.82, 368.31, and 648.00 a.u for the 0.05, 0.1, 0.5 µg/ml of the sample concentrations, respectively. The results showed that the modified FSNP-anti-IgY may be used for the fluorescence detection of antibodies.

Effect of xanthyletin on the structural and fluorescence properties of a silica-based hybrid composite

This work studied the fluorescence emission and the structural properties of a hybrid composite based on a silica matrix with embedded xanthyletin. The xanthyletin was easily extracted from the Brosimum rubescens wood using ethyl alcohol. Results for the as-obtained extract from nuclear magnetic resonance (NMR) showed a high amount of a compound identified as xanthyletin (C14H12O3). The extracted xanthyletin was embedded into a silica matrix using the sol-gel method. The evolution of the fluorescence emission and structural properties were analyzed for the hybrid composite as the temperature increased from RT to 1000 °C. Results show that the interaction between the organic and inorganic components gives an increment of one magnitude order in the fluorescence emission concerning the xanthyletin in the ethyl alcohol. Also, the fluorescence reached its maximum intensity in the sample heat-treated at 200 °C. This behavior is ascribed to the interactions between the xanthyletin and the silica matrix. In addition, the embedded xanthyletin induces a structural rearrangement in the silica matrix. Thus, the fluorescence intensity appears to show a close relationship with the Si–O network arrangement.

Incorporation of Upconverting LiYF4:Yb3+, Tm3+ Nanoparticles with High Quantum Yield in TiO2 Metallogels for Near Infrared-Driven Photocatalytic Dye Degradation

By using anhydrous conditions, we report here an optimized synthesis of small but highly emitting upconverting nanoparticles (UCNPs) of LiYF4:Yb3+, Tm3+ without any surface passivation layers of silica or undoped matrix. For this, anhydrous precursors [Li(TFA)(monoglyme)] and [Ln(TFA)3(monoglyme)] (Ln = Y, Gd, Tm, Yb; TFA = trifluoroacetate) were synthesized via a facile one-pot synthetic protocol, which showed excellent thermal decomposition compatibility to afford Ln3+-doped LiLnF4 NPs by simultaneous decomposition in the solution phase. A detailed study of the influence of many key parameters such as the ratio of dopant ions and solvents, concentration of precursors, reaction time, and temperature over crystalline phase, size, shape, morphology, and upconverting properties of the NPs produced followed by a mechanism for the formation of LiYF4-based NPs is presented. The high quality of these NPs is manifested by the fact that their upconversion efficiency is quite comparable to that of a bulk single crystal of the same composition (bulk materials are believed to have far better UC performance due to low surface area and less defects). Successful incorporation of these UCNPs in transparent TiO2 metallogels provided an alternative strategy of highly homogeneous UCNP-TiO2 composites of variable composition (1–10% of NPs) having very high specific surface area (435–580 m2/g).

Bacterial cell immobilized packed bed reactor for the elimination of dissolved organics from biologically treated post-tanning wastewater and its microbial community profile

In conventional, the biologically treated tannery wastewaters are rich in dissolved organics and the application of reverse osmosis (RO) to biologically treated tannery wastewater was challenged with fouling and failure of RO membrane due to existence of lingering dissolved organic compounds. In present investigation the bacterial cell immobilized packed bed reactor (CIPBR) was operated to remove the dissolved organic compounds in biologically treated post-tanning wastewater to avoid membrane fouling in RO. The efficient microbial syndicate to eliminate dissolved organics in post-tanning wastewater was isolated and immobilized on to the carbon silica matrix (CSM) in the range of 2.98 ± 0.2 × 107 cells gm−1 of CSM and the same was used as a carrier matrix in the packed bed reactor. The CIPBR established the CODtot, CODdis and BOD removal efficiency by 61 ± 4%, 57 ± 4% and 87 ± 3% respectively with CODtot, CODdis and BOD remained in the treated wastewater as 236 ± 21 mg/L, 228 ± 21 mg/L, and 12 ± 3 mg/L under continuous operation. The removal of dissolved organic compounds from the post-tanning wastewater was confirmed using UV–Visible and FT-IR spectroscopic studies. Among the total microbial community, the phylum Proteobacteria played most abundant role with 48.47% of relative abundance for the removal of dissolved organics in biologically treated post-tanning wastewater. The significance of the study is to replace the tertiary treatment unit operation in the conventional ETP/CETP to remove dissolved organics in wastewater.

Ultra‐Stable and Highly Efficient White Light Emitting Diodes through CsPbBr3 Perovskite Nanocrystals−Silica Composite Phosphor Functionalized with Surface Phenyl Molecules (Small 7/2023)

White Light Emitting Diodes of Perovskites In article number 2206311, Kyoungja Woo and co-workers present the white light emitting diodes (LEDs) incorporating CsPbBr3 NCs–SiO2Ph phosphor, which exhibit unprecedented stability and high efficiency during continuous operation. The high stability and performance originate from grain growth and striking photoluminescence-enhancement, upon thermal curing/aging, of the NCs encapsulated in a compact silica matrix, which is impermeable to H2O but permeable to O2. The synthesis strategy herein provides a realistic pathway toward perovskite NC-based phosphors for practical applications.

Synthesis of polystyrene derivative‐silica hybrids via in situ thiol‐ene reaction in the sol–gel process

AbstractPolystyrene derivative‐silica hybrids are synthesized via an in situ thiol‐ene reaction in the sol–gel process. Poly(p‐(3‐butenyl)styrene) (PBSt) which is a polymer having vinyl groups in its repeating units is used as an organic polymer and 3‐mercaptopropyltriethoxysilane (MPTES) is used as a photo‐induced crosslinking agent between the organic polymer and the silica matrix. MPTES is introduced to PBSt via a thiol‐ene reaction by the UV irradiation. Simultaneously, an acid catalyzed sol–gel reaction of tetraethoxysilane (TEOS) proceeds. The obtained hybrids having the organic polymer content of 30%, 50%, and 70% are optically transparent. On the other hand, the hybrids synthesized without the UV irradiation are turbid or translucent. The SEM–EDX analyses of the transparent hybrids show the homogeneity of the polymer and the silica in the hybrids. These results indicate that forming covalent bonds between PBSt and silica matrix through MPTES by the UV‐promoted thiol‐ene reaction improves the homogeneity of the hybrids. The thermal analyses of the hybrids using TGA show the silica components are almost quantitatively introduced into the resulting hybrids. The DSC measurements show that the resulting hybrids have higher Tg than the original organic polymer.

Phosphorescent Carbon Dots as Long-Lived Donors To Develop an Energy Transfer-Based Sensing Platform.

Employing long-lived luminescent materials to design a chemical sensing platform can eliminate real-time excitation and background fluorescence. However, the realization of long-lived emissions in aqueous media was limited to transition-metal complexes, doped quantum dots, organic crystals, and inorganic persistent phosphors, which suffer from the drawbacks of large size, expensive elements, and poor dispersibility. In this work, phosphorescent carbon dots (CDs) were covalently immobilized in a silica matrix (CDs@SiO2) to achieve afterglow emission in an aqueous dispersion. CDs@SiO2 with long lifetime (∼1.6 s) was utilized as an energy donor to fabricate nonradiative energy transfer systems with various organic dyes through the surface micelle self-assembly method. Benefiting from the high energy transfer efficiency between CDs@SiO2 and organic dyes, multicolor afterglow emissions were successfully obtained in aqueous media. As a proof of concept, a ratiometric phosphorescent probe using CDs@SiO2 as a donor and Hg2+-responsive rhodamine derivative as an acceptor was designed. Hg2+ triggered the energy transfer process between the donor-acceptor pair, leading to the sensitive detection of Hg2+ ions. The work presented here provides opportunities to develop chemical sensors with low background interferences and easily recognizable signals.

Mesoporous zeolite Beta supported Ni nanoparticles for the catalytic hydroconversion of extraction portion from Jinjitan subbituminous coal to cycloalkanes

The catalytic hydroconversion (CHC) of heavy carbon organic species (HCOSs) to cycloalkanes represents an importantly used chemical industry process due to the wide applicability of the resulting products in energy and fine chemistry. Despite the existing conventional catalysts applied to the CHC of HCOSs, the development of highly active bifunctional Ni-based heterogeneous catalysts for this process is still a challenge. Therefore, we show that the modified deposition–precipitation of nickel (II) nitrate on hydrothermally synthesized mesoporous zeolite Beta (MZB) prepares a Ni/MZB catalyst with a through-crosslinking mesopore structure and uniformly disperse Ni nanoparticles (NPs) at rough MZB crystal surface. The 10%Ni/MZB (10% Ni loading), in the presence of exposing on amount of accessible Lewis acid sites (LASs) and attaching Ni NPs by chemical bonding from the silica matrix of MZB skeleton, exhibits excellent activity to promote the CHC of all kind of aromatic rings and heteroatom-containing species, including chain alkanes, arenes, oxygen-containing organic compounds (OCOCs), nitrogen-containing organic compounds (NCOCs), and sulfur-containing organic compounds (SCOCs), to produce cycloalkanes and hydroarenes under mild conditions. Interestingly, density functional theory (DFT) calculations indicate that the transfer of biatomic active hydrogen (H…H) and heterogenous H+ from 10%Ni/MZB plays important roles during the CHC of diphenoxybenzene (DPOB). After being recycled 4 times, 10%Ni/MZB is still maintains high activity for CHC of DPOB under mild conditions.

Spectroscopic studies on phosphate-modified silicon oxycarbide-based amorphous materials

Vibrational spectroscopy is the most effective, efficient and informative method of structural analysis of amorphous materials with silica matrix and, therefore, an indispensable tool for examining silicon oxycarbide-based amorphous materials (SiOC). The subject of this work is a description of the modification process of SiOC glasses with phosphate ions based on the structural examination including mainly Infrared and Raman Spectroscopy. They were obtained as polymer-derived ceramics based on ladder-like silsesquioxanes synthesised via the sol-gel method. With the high phosphate’s volatility, it was decided to introduce the co-doping ions to create [AlPO4] and [BPO4] stable structural units. As a result, several samples from the SiPOC, SiPAlOC and SiPBOC systems were obtained with various quantities of the modifiers. All samples underwent a detailed structural evaluation of both polymer precursors and ceramics after high-temperature treatment with Fourier-transformed infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD) and magic angle spinning nuclear magnetic resonance (MAS-NMR). Obtained results proved the efficient preparation of desired materials that exhibit structural parameters similar to the unmodified one. They were X-ray-amorphous with no phase separation and crystallisation. Spectroscopic measurements confirmed the presence of the crucial Si-C bond and how modifying ions are incorporated into the SiOC network. It was also possible to characterise the turbostratic free carbon phase. The modification was aimed to improve the bioperformance of the materials in the context of their future application as bioactive coatings on metallic implants.

Aerogel-Based Single-Ion Magnets: A Case Study of a Cobalt(II) Complex Immobilized in Silica

The chemical immobilization of cobalt(II) ions in a silica aerogel matrix enabled the synthesis of the first representative example of aerogel-based single-ion magnets. For the synthesis of the lyogels, methyl-trimethoxysilane and N-3-(trimethoxysilyl)propyl ethylenediamine were co-hydrolyzed, then the ethylenediamine groups that were immobilized on the silica matrix enabled the subsequent binding of cobalt(II) ions. Lyogels with various amounts of ethylenediamine moieties (0.1-15 mol %) were soaked in isopropanol solutions of cobalt(II) nitrate and further supercritically dried in carbon dioxide to obtain aerogels with a specific surface area of 210-596 m2·g-1, an apparent density of 0.403-0.740 cm3·g-1 and a porosity of 60-78%. The actual cobalt content in the aerogels was 0.01-1.50 mmol per 1 g of SiO2, which could easily be tuned by the concentration of ethylenediamine moieties in the silica matrix. The introduction of cobalt(II) ions into the ethylenediamine-modified silica aerogel promoted the stability of the diamine moieties at the supercritical drying stage. The molecular prototype of the immobilized cobalt(II) complex, bearing one ethylenediamine ligand [Co(en)(MeCN)(NO3)2], was synthesized and structurally characterized. Using magnetometry in the DC mode, it was shown that cobalt(II)-modified silica aerogels exhibited slow magnetic relaxation in a nonzero field. A decrease in cobalt(II) concentration in aerogels from 1.5 mmol to 0.14 mmol per 1 g of SiO2 resulted in a weakening of inter-ion interactions; the magnetization reversal energy barrier likewise increased from 4 to 18 K.

Ultrasound‐assisted synthesis of silica‐coated magnetite material decorated with silver nanoparticles for the detoxification of 4‐nitrophenol

Among phenolic pollutants, 4‐nitrophenol is a common organic pollutant readily discharged in water bodies. It causes an adverse effect on the lives of human beings and aquatic species. Therefore, it is essential to remove this pollutant from water resources. Herein, we report an eco‐friendly approach for the synthesis of silica‐coated magnetite material decorated with ultra‐fine silver nanoparticles, as a magnetically recyclable catalyst for the detoxification of 4‐nitrophenol. This synthetic strategy employs only ultrasound waves throughout the preparation of catalyst material. Further, no stabilizer was added in any of the steps involved in synthesis. Initially, iron oxide nanoparticles were synthesized from ferrous sulphate heptahydrate precursor and coated with silica matrix. Subsequently, silver nanoparticles were deposited over it. Silver was chosen among the noble metal nanoparticles, as it is abundantly available and economical and exhibits good catalytic properties. This catalyst material was well characterized using HRTEM, XRD, VSM and FTIR techniques. HRTEM studies revealed that Ag nanoparticles of size between 2 and 5 nm were dispersed over the silica‐coated magnetite. The significant merits of this approach are usage of ultrasound waves, stabilizer‐free and reduced time consumption in the synthesis of catalyst. Furthermore, a facile magnetic separation of catalyst using bar magnet is noteworthy to this method. The catalyst was successfully recycled for eight times without any significant loss in the activity. This can be a promising catalyst for the treatment of wastewater contaminated with 4‐nitrophenol.