Novel γ-Fe2O3-nanoparticle (NP) modified N-doped porous carbon materials (γ-Fe2O3/mCN) were prepared by one-pot pyrolysis of a mixture of melamine, polyacrylonitrile, and FeCl3·6H2O at different temperatures. At a pyrolysis temperature of 900 °C, γ-Fe2O3/mCN-900-20 exhibited a high surface area and a N content of 8.47%, caused by the complete pyrolysis of melamine and polyacrylonitrile at 900 °C. The obtained material γ-Fe2O3/mCN-900-20 was used as a cost-effective catalyst for the hydrogenation of nitrobenzene using N2H4·H2O as the reductant under mild reaction conditions. As compared to other catalysts (e.g., noble metal catalysts), γ-Fe2O3/mCN-900-20 exhibited high catalytic performance (TOF of 311.83 h−1, selectivity of 100%). During the catalytic hydrogenation of nitroaromatic compounds with reducible groups, e.g., alcoholic hydroxyl, halogen, and amino groups, an excellent selectivity close to 100% was achieved. Moreover, because the active sites of γ-Fe2O3 has magnetic performance, the catalyst can be easily recovered using a magnet, and reused at least four runs without an obvious activity decrease. Hence, the easily prepared, cost-effective and reusable γ-Fe2O3/mCN catalyst fabricated in this study demonstrates potential for applications in selective reduction of aromatic nitro compounds.

Efficient chemoselective hydrogenation of halogenated nitrobenzenes using low-cost catalysts is an important research area of applied catalysis. In this work, a Fe metal organic gel (Fe-MOG) was prepared via metal coordination interaction between Fe(NO3)3·9H2O and 1,4-naphthalenedicarboxylic acid. Fe-MOG was used as the precursor for the fabrication of a low-cost γ-Fe2O3-modified mesoporous carbon catalyst (γ-Fe2O3/MC) through carbonization under an N2 atmosphere at high temperature. The obtained γ-Fe2O3/MC catalyst had high catalytic activity and selectivity for the hydrogenation of Cl−, Br− and I− functionalized nitrobenzenes without any obvious dehalogenation. The hydrogenation reactions had a product yield and selectivity for the corresponding halogenated aniline of 100% when using hydrazine hydrate as the reducing agent. The whole hydrogenation reaction process was environmentally friendly because of its harmless byproducts (H2O and N2). In addition, the γ-Fe2O3/MC catalyst was recyclable because of the magnetism of the γ-Fe2O3 active sites. The catalytic activity of the γ-Fe2O3/MC catalyst was not obviously decreased after being recycled five times. Therefore, the γ-Fe2O3/MC catalyst has great potential for future applications in the chemoselective hydrogenation of halogenated nitrobenzenes.

Inexpensive and reusable transition metal heterogeneous catalysts exhibiting excellent catalytic performance represent an attractive alternative to noble metal and homogeneous catalysts. In this work, we fabricated a novel nanocatalyst comprised of Co nanoparticles (NPs) supported on a N-doped mesoporous carbon (Co/mCN-900) by simple one-pot pyrolysis of a homogeneous mixture of melamine, polyacrylonitrile, and Co(NO3)2·6H2O under a N2 atmosphere at 900 °C. The as-obtained Co/mCN-900 catalyst displayed a fluffy mesoporous structure with highly dispersed and accessible Co NPs acting as catalytic active sites. The Co/mCN-900 catalyst was effective in hydrogenating nitroarenes at milder conditions (i.e., 1 MPa H2 and 120 °C) as compared to previously reported Co- and Ni-based catalysts. The Co/mCN-900 catalyst also catalyzed the reductive N-alkylation of nitroarenes with carbonyl compounds to form the corresponding aromatic secondary amines under very mild reaction conditions. In addition, the Co/mCN-900 catalyst showed good reusability since its morphology and activity were maintained after several reaction cycles. Therefore, this work provides a facile and promising method for fabricating non-precious transition metal-based catalysts with excellent performance and great potential for sustainable chemistry applications.The Co/mCN-900 catalyst that was prepared by simple one-pot pyrolysis of the homogeneous mixture of melamine, polyacrylonitrile and Co(NO3)2·6H2O under N2 atmosphere can be used for catalytic hydrogenation of nitroarenes and direct reductive N-alkylation of nitroarenes with carbonyl compounds.Download high-res image (170KB)Download full-size image

Novel fluffy smoke like mesoporous N-doped carbon (mNC) was prepared through a facile one-pot carbonization method using the low-cost melamine and polyacrylonitrile as the precursor materials. The obtained mNC material exhibits a high surface area, rich nitrogen content and can be used as an ideal catalyst support to fabricate noble metal modified nanocatalysts. Here, small Ag nanoparticles were supported on the mNC material with high dispersion to give the Ag/mNC nanocatalyst. The obtained Ag/mNC nanocatalyst was used in the catalytic reduction of nitroarenes and showed excellent catalytic activity, probably due to the small Ag NPs which highly dispersed on the fluffy mNC material that can enhance the accessibility and mass transfer, and subsequently enhance the catalytic activity. It is worth mentioning that, in the catalytic reduction of nitroarenes with halogenated groups, almost no dehalogenation phenomenon can be observed, which implies the superior catalytic chemoselectivity of the Ag/mNC nanocatalyst.A novel fluffy smoke like mesoporous N-doped carbon (mNC) was prepared through a facile one-pot carbonization method using the low-cost melamine and polyacrylonitrile as the precursor materials and was modified by small Ag nanoparticles to fabricate the Ag/mNC nanocatalyst. The obtained Ag/mNC nanocatalyst was used in the catalytic reduction of nitroarenes and showed excellent catalytic activity and reusability.Download high-res image (87KB)Download full-size image

•Co NPs decorated N-doped mesoporous carbon was prepared by a simple one-pot pyrolysis method.•Metallic Pt was covered on the surface of the Co NPs through a replacement reaction.•Pt@Co/mCN showed excellent activity in the catalytic hydrogen release from ammonia borane.Ammonia borane (NH3BH3, AB) is considered as an excellent chemical material for the hydrogen storage attribute to its high hydrogen storage capacity. However, developing highly efficient catalysts for continuous hydrogen generation from AB is still a challenge for the future fuel cell applications. Initially, a facile one-pot carbonization method was used for fabrication cobalt nanoparticles (Co NPs) doped fluffy N-doped mesoporous carbon (Co/mCN). Further, the Pt@Co/mCN nanocatalyst was prepared through a facile spontaneous displacement reaction by using the Co/mCN material and H2PtCl6 as the starting materials. Here, the metallic Pt only covered on the surface of the Co NPs in the view of Pt saving. The Pt@Co/mCN nanocatalyst was used in the catalytic hydrogen generation from AB and showed excellent catalytic activity and reusability. The superior catalytic activity of the Pt@Co/mCN nanocatalyst is probably due to the isolated Pt atoms on the surface of the Co NPs and the highly dispersed Pt@Co NPs on the surface of the fluffy mCN support.The Pt@Co/mCN nanocatalyst was prepared through a facile method and used in the catalytic hydrogen generation from AB and showed excellent catalytic activity and reusability.Download high-res image (273KB)Download full-size image

•Ultrafine Pt nanoparticles were modified on cotton derived carbon fibers with high dispersity.•The starting materials for the fabrication of target catalysts is cheap and green.•The obtained Pt/CCF catalyst was used for the hydrolysis of AB for hydrogen production.•The Pt/CCF catalyst exhibits excellent catalytic activity and reusability.Hydrogen is regarded as the cleanest energy in future. One of the most promising routes for the production of hydrogen is catalytic hydrolysis of ammonia borane due to it is a highly efficient and safe method. Developing efficient catalysts for large-scale industrial application in the hydrolysis of ammonia borane recently is highly demanded. In this work, we designed a facile synthesis strategy that takes advance of the excellent hydrophilic of cotton cellulose fiber that can efficiently adsorb platinum ions on the fiber surface. Then, the platinum ions adsorbed cotton fibers were freeze-dried and carbonized under nitrogen atmosphere to fabricate the ultrafine platinum nanoparticles (Pt NPs) modified catalysts (Pt/CCF). It was found that, the carbonization temperatures greatly influenced the dispersion and the particle size of Pt NPs; under carbonization at 500 °C, the obtained Pt(8%)/CCF-500 catalyst has highly dispersed ultrafine Pt NPs. The prepared Pt/CCF catalysts have been tested for the hydrolysis of AB for hydrogen production. And the Pt(8%)/CCF-500 catalyst exhibited excellent catalytic performance under mild reaction conditions. The catalyst exhibits higher catalytic activity (TOF value of 35 mol H2 mol−1 Pt min−1) and lower activation energy (Ea) value of 39.2 kJ mol−1 than most of other Pt based catalysts. This simple synthesis method may provide a useful platform for the large-scale application of cotton derived carbon materials supported noble metal catalysts.Ultrafine platinum nanoparticles were highly dispersed on the cotton derived carbon fibers and used as a highly efficient catalyst for catalyze hydrolysis of ammonia borane.Download high-res image (320KB)Download full-size image

•A novel yolk–shell-structured material Fe3O4@γ-AlOOH-YSMs has been prepared.•The Fe3O4@γ-AlOOH-YSMs has hierarchical γ-AlOOH flakes as the mesoporous shell.•The Pd/Fe3O4@γ-AlOOH-YSMs nanocatalyst exhibited excellent catalytic activity.•The Pd/Fe3O4@γ-AlOOH-YSMs nanocatalyst also can be easily recovered and reused.A novel yolk–shell-structured material (Fe3O4@γ-AlOOH-YSMs) with hierarchical γ-AlOOH flakes as the mesoporous shell and Fe3O4 nanoparticles (NPs) in the hollow core was prepared by using Fe3O4@SiO2 NPs as the seeds as well as NaAlO2 and urea as the precursor. The prepared Fe3O4@γ-AlOOH-YSMs were used as a catalyst support for fabricating a Pd/Fe3O4@γ-AlOOH-YSMs nanocatalyst with no obvious aggregation of the Pd NPs. The Pd/Fe3O4@γ-AlOOH-YSMs nanocatalyst was utilized for the catalytic reduction of the widely used and highly toxic 4-nitrophenol, rhodamine B, methylene blue, and methyl orange; and showed excellent catalytic activity as compared with other noble-metal-based catalysts. Furthermore, the Pd/Fe3O4@γ-AlOOH-YSMs nanocatalyst also can be easily separated from the reaction mixture and reused for at least ten times without any obvious decrease in the catalytic activity, indicating its reusability and stability.Download high-res image (78KB)Download full-size image

•Pt NPs were immobilized in the core of mesoporous silica-coated magnetic nanocapsules.•The Fe3O4@SiO2@Pt@mSiO2 catalyst was used for the hydrolysis of AB for hydrogen production.•Pt leaching can be efficiently prevented during catalytic process.•The catalyst could be effortlessly recovered by an external magnet.In this work, novel hollow mesoporous silica-coated magnetic nanocapsule that immobilizing Pt nanoparticles (NPs) in its core (Fe3O4@SiO2@Pt@mSiO2) was successfully synthesized. The obtained catalyst was characterized by TEM, XRD, BET, VSM, ICP and N2 adsorption-desorption. The Fe3O4@SiO2@Pt@mSiO2 catalyst was used in the catalytic hydrogen generation from hydrolysis of ammonia borane and showed superior catalytic activity. Moreover, the Fe3O4@SiO2@Pt@mSiO2 catalyst can be easily recovered by magnetic separation attributed to the supermagnetic Fe3O4 NPs imbedded in the inner core. It is worth mentioning that, due to the Pt NPs were immobilized in the core of the nanocapsules and covered with mesoporous silica shell, Pt NPs leaching was efficiently prevented during the catalytic process. Therefore, this work provided a helpful platform for the preparation of noble metal based nanostructured catalysts with excellent activity, accessibility, facile recovery and almost no noble metal leaching.Download high-res image (297KB)Download full-size image

An N-doped mesoporous carbon supported Ni nanoparticle nanocatalyst (Ni/m-CN) was prepared in a facile manner by the carbonization of Ni-MOFs. The Ni/m-CN nanocatalyst exhibited excellent catalytic activity for the reduction of nitroarenes under mild conditions. Moreover, the Ni/m-CN nanocatalyst can also be easily recovered and reused due to its superparamagnetism.

•N-doped magnetic mesoporous carbon was prepared through carbonization of Ni MOF.•Pd/Ni-mCN catalyst showed high catalytic activity in HDC of chlorophenols.•Pd/Ni-mCN catalyst exhibited high catalytic stability and efficient recyclability.Ni MOF-derived N-doped magnetic mesoporous carbon-supported Pd nanoparticles (Pd/Ni-mCN) were prepared and used in the hydrodechlorination (HDC) of chlorophenols (CPs) water pollutants with H2 at mild reaction conditions. The Pd/Ni-mCN catalyst was characterized in detail by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), N2 adsorption/desorption, and vibrating sample magnetometry (VSM). The Pd/Ni-mCN nanocatalyst showed high activity and complete HDC conversion of a target pollutant such as 4-CP after 90 min at ambient conditions. Other CPs compounds such as 2-CP, 3-CP, 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) were also tested in the HDC reaction. 2-CP was the only intermediate product in the HDC of 2,4-DCP, with phenol being the final product. The HDC of 2,4,6-TCP proceeded with the intermediate formation of 2-CP and 2,4-DCP, this being potentially originated from the steric hindrance of the ortho-substituted Cl atom. Additionally, Pd/Ni-mCN exhibited high catalytic stability and recyclability. Thus, Pd/Ni-mCN was successfully recycled owing to its superparamagnetic properties and reused for at least five times showing stable conversions (above 99% at 90 min) the HDC of 4-CP.

We present a facile route for the fabrication of palladium modified magnetic nanoparticles (Fe@Pd NPs) embedded in mesoporous carbon (MC), derived from metal–organic frameworks, to produce the Fe@Pd–MC nanocatalyst. The Fe@Pd–MC nanocatalyst exhibited excellent catalytic activity toward the hydrogenation of nitroarenes as well as easy recovery and reusability.

Dendritic mesoporous silica nanospheres (DMSNs) have been synthesised in this work. The distance of each “arborization” is 7 nm, which plays the role of “pore”. Hydrodechlorination (HDC) of 4-chlorophenol (4-CP) as the target compound using Pd modified DMSNs as the catalyst (Pd/DMSNs) is carried out in aqueous sodium hydroxide solution under atmospheric H2 pressure, fairly mild conditions for a potential application to treat industrial wastewater. Compared with some supported Pd catalysts, Pd/DMSNs exhibit an improved catalytic performance, owing to the specific dendritic structure, which can improve mass transfer, and increase the adsorption–desorption rate of compounds. In this work, both the dechlorination process and further hydrogenation process of 4-CP are studied under various conditions including different catalyst dosages and different temperatures. By analyzing the experimental results, it is clear that the influential factors mentioned above have a strong impact on the selectivity of the HDC experiment. In addition, 2-CP, 3-CP, and 2,4-DCP are also tested as target pollutants.

Recently, catalysts with easily accessible active sites and high efficiency and recyclability have triggered various research interests. In this study, we prepared uniform fibrous silica microspheres with a γ-Fe2O3 magnetic core (γ-Fe2O3@SiO2@KCC-1) as the catalyst support. The distance between two fibers was approximately 10–20 nm. Au nanoparticles (NPs) were highly dispersed on the silica fibers without aggregation to form the nanocatalyst Au/γ-Fe2O3@SiO2@KCC-1. The catalytic activity of Au/γ-Fe2O3@SiO2@KCC-1 for the reduction of 4-nitrophenol (4-NP) with NaBH4 was measured by UV-vis spectroscopy. Au/γ-Fe2O3@SiO2@KCC-1 exhibited better catalytic activity toward the reduction of 4-NP compared with other reported Au NP-based catalysts. The high catalytic activity was mainly attributed to the easy accessibility of the Au NPs of the prepared nanocatalyst. In addition, Au/γ-Fe2O3@SiO2@KCC-1 could be easily recycled by applying an external magnetic field while maintaining the catalytic activity without significant decrease even after six runs. The unique properties provided an ideal platform to study various noble metal/γ-Fe2O3@SiO2@KCC-1 nanocatalysts that can be potentially applied in a wide variety of fields such as catalysis and green chemistry.

In this study, a novel core–shell magnetic fibrous nanocatalyst, Pd/Fe3O4@SiO2@KCC-1 with easily accessible active sites and a convenient recovery by applying an external magnetic field, was successfully developed. Fe3O4@SiO2@KCC-1 was functionalized with amino groups which act as robust anchors so that the palladium nanoparticles (Pd NPs) with an average diameter of about 4 nm were well-dispersed on the fibers of Fe3O4@SiO2@KCC-1 without obvious aggregation. The synthesized Pd/Fe3O4@SiO2@KCC-1 nanocatalyst exhibited excellent catalytic activity in the reduction of 4-nitrophenol by sodium borohydride, and the Suzuki cross coupling reactions of aryl chlorides with aryl boronic acids due to the easy accessibility of the active sites. Furthermore, the Pd/Fe3O4@SiO2@KCC-1 nanocatalyst was conveniently recovered by a magnet and could be reused for at least five cycles without significant loss in activity, thus confirming its good stability. Therefore, the abovementioned approach based on core–shell magnetic fibrous Fe3O4@SiO2@KCC-1 provided a useful platform for the fabrication of Pd NPs based catalysts with easy accessibility, superior activity and convenient recovery.

The development of low cost noble metal nanocatalysts with high activity and selectivity, high catalytic performance, convenient separation, and reusability is a significant challenge. Herein, the magnetic porous carbon (MPC) composite synthesized from metal organic framework (MOF) was used as a catalyst support to fabricate gold (Au) and palladium (Pd) nanoparticle (NP) based nanocatalysts. The MPC not only provided a large surface area and mesopores on which the active centers (Au and Pd NPs) were finely dispersed, but also exhibited superparamagnetic behaviour that enabled the magnetic separation and convenient recovery of the nanocatalysts from the reaction mixture. Thus, the nanocatalysts were repeatedly used without loss of catalytic efficiency. Both the Au/MPC and Pd/MPC nanocatalysts showed excellent catalytic activity for the reduction of 4-nitrophenol. Moreover, the Pd/MPC nanocatalyst exhibited higher efficiency toward hydrodechlorination of 4-chlorophenol compared to the other reported catalysts. This study indicated that the noble metal NPs (NMNPs) supported on MOF-derived MPC materials could act as promising catalysts exhibiting potential applications in numerous NMNP based catalytic reactions.

A novel selective fluorescent chemosensor (L1) based on 8-aminoquinoline was synthesized and characterized. The sensor exhibited remarkable selectivity for Zn2+ in the presence of other cations in aqueous solution. Density functional theory calculations on L1 and the L1–Zn complex are consistent with the experimental results. Once combined with Zn2+, the complex L1–Zn displayed high specificity for H2S. As HS− is equivalent to H2S in physiological solution, HS− was selected to represent H2S in this work. Among various anions, only HS− induced revival of the fluorescence of L1. Signal transduction occurs via reversible formation–separation of complex L1–Zn and ZnS. L1 and the sequential complex L1–Zn have ideal chemical and spectroscopic properties that satisfy the criteria for further Zn2+ and H2S sensing in biological and environmental applications.

A Schiff base-type fluorescent chemosensor L has been synthesized and characterized to relay recognition of Zn2+ and H2S. Among various metal ions, only Zn2+ induces the fluorescence enhancement of the sensor L and results in an “Off–On” type sensing with excellent selectivity and high sensitivity in aqueous solution. The lowest detection limit for Zn2+ is 1 × 10−7 M. Density functional theory calculation for L and the resultant zinc complex is also performed in this study. The chemosensor also exhibits fluorescence quenching with Cu2+ in aqueous solution. Fluorescent changes of L upon the addition of Zn2+ and Cu2+ is utilized as an INHIBIT logic gate at the molecular level, using Zn2+ and Cu2+ as chemical inputs and the fluorescence intensity signal as the output. On the other hand, the consequent product of L and Zn2+, L–2Zn, is an excellent indicator for H2S for displacement of Zn2+ from the complex L–2Zn. Its H2S sensing behavior is not interfered with by reduced glutathione (GSH), L-cysteine (L-Cys), and even bovine serum albumin (BSA) indicates that L–2Zn is able to detect H2S without any distinct interference from these biological thiols. The addition of H2S leads to the fluorescence quenching of L–2Zn, forming an “On–Off” type sensing system. Therefore, the sensing process for Zn2+ and sequential detection of H2S is a reversible one, and also constitutes an “Off–On–Off” type fluorescence monitoring system. This Zn2+ and H2S sequential recognition via fluorescence relay enhancement and quenching give probe L the potential utility for Zn2+ and H2S detection in aqueous media and biological samples.

•Ni@Au NPs were well-dispersed on the fibers of the KCC-1 without aggregation.•Ni@Au/KCC-1 nanocataly with easy accessibility owing to its fibers and not pores.•Ni@Au/KCC-1 showed excellent catalytic activity in reduction of nitro-compounds.•Ni@Au/KCC-1 could be easily reused for ten times without losing catalytic activity.A novel, dandelion-like fibrous nano-silica catalyst (Ni@Au/KCC-1) has been synthesized by modifying fibrous nano-silica (KCC-1) with Ni@Au core–shell nanoparticles (NPs). KCC-1 was prepared using a hydrothermal method and has a dandelion-like shape, high surface area, and easy accessibility; KCC-1 can also be functionalized with 3-mercaptopropyltriethoxysilane. The mercaptopropyl groups on the fibers act as robust anchors for the immobilization of Ni@Au NPs, thus preventing the aggregation of the Ni@Au NPs. We investigated the catalytic performance of the Ni@Au/KCC-1 nanocatalyst by reducing 4-nitrophenol to 4-aminophenol in the presence of NaBH4 as a probe reaction. The resulting Ni@Au/KCC-1 nanocatalyst exhibited superior catalytic activity to Ni@Au NPs, which may be attributed to the high accessibility of the KCC-1 support material. To some extent, it also may be due to the poor aggregation of Ni@Au NPs on the KCC-1 nano-silica support. The Ni@Au/KCC-1 nanocatalyst also showed high catalytic activity when used to reduce 2-nitroaniline. It is noteworthy that using Ni cores to fabricate the active sites Ni@Au NPs resulted in a lower amount of Au needed than is typical, because most of the Au-NPs catalyzed reactions occur on the surfaces of the NPs. In addition, the Ni cores give the Ni@Au/KCC-1 nanocatalyst superparamagnetic properties that increase its ease of recovery by a powerful magnet, allowing for it to be reused. The abovementioned approach based on fibrous KCC-1 and Ni@Au NPs provided a useful platform for the fabrication of noble-metal-based nanocatalysts with easy accessibility and a low cost, which may allow for an efficient green alternative for various catalytic reductions.

A novel and simple fluorescent chemosensor based on rhodamine (R-2) is designed and synthesized to detect Hg2+. Probe R-2 exhibits high selectivity and sensitivity for sensing Hg2+ with a detection limit at 10−8 M level, and displays a significant color change from colorless to pink color in the presence of Hg2+. About a 400-fold increase in fluorescence emission intensity is observed upon binding excess Hg2+ in 50% H2O/CH3CN HEPES buffer at pH 7.00. The titration results show a 1:1 complex formation between R-2 and Hg2+. The reversibility of chemosensor R-2 is verified through its spectral response toward Hg2+ and I− titration experiments. Using Hg2+ and I− as chemical inputs and the fluorescence intensity signal as outputs, R-2 can be utilized as an INHIBIT logic gate at molecular level.Highlights► A Hg2+ sensor (R-2) has been developed based on rhodamine B. ► The sensor has high fluorescent selectivity for Hg2+ over various competitive cations. ► R-2 is recyclable when adding I− to the solution of Hg2+/R-2. ► Using Hg2+ and I− as inputs, R-2 could be used as an INHIBIT logic gate.

In the present work, a novel dansyl group functionalized Fe3O4@SiO2 magnetic nanomaterial with a core–shell structure was developed, aiming to detect and remove Hg2+ from aqueous media. The multifunctional nanocomposite shows excellent fluorescence sensitivity and selectivity towards Hg2+ over other metal ions (Na+, K+, Mg2+, Al3+, Ca2+, Cd2+, Ni2+, Co2+, Fe3+, Zn2+, Pb2+, Cu2+, Ag+). Concentrations as low as 10−8 M can be detected and the addition of other metal ions has a negligible influence on the fluorescence emission. Regarding the reversibility of the nanosized sensor, the fluorescence of the DAP-Fe3O4@SiO2 nanocomposite in the presence of Hg2+ ions is found to be almost reversible when treated with iodide anion. Additionally, the nanocomposite can be easily separated from solutions by adding an external magnetic field. Moreover, the functionalized nanosphere shows a good adsorption capacity to Hg2+, which makes it repeatedly applicable for simultaneous Hg2+ sensing and removal from polluted water. These results indicate that the multifunctional nanocomposite may find potential applications for simple detection and easy removal of Hg2+ in biological and environmental areas.

•Uniform magnetic SiO2@Fe3O4@m-MnO2 microspheres with mesoporous MnO2 shell were prepared.•The Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst exhibited excellent catalytic activity.•The Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst also can be easily recovered and reused.In this study, magnetic SiO2@Fe3O4@m-MnO2 microspheres with uniform morphology and mesoporous MnO2 shell were successfully prepared. The MnO2 sheets structured mesoporous shell could provide a large specific surface area, thereby increasing the catalytically active sites. Thus, magnetic SiO2@Fe3O4@m-MnO2 microspheres were used as a catalyst support. Palladium nanoparticles (Pd NPs) were successfully anchored with high dispersion on SiO2@Fe3O4@m-MnO2 surface, successfully obtained Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst with a Pd weight percentage of 6%. The obtained nanocatalyst was employed in the hydrodechlorination of highly toxic 2,4-dichlorophenol and catalytic reduction of the widely used nitroaromatics and organic dyes under ambient conditions. In these catalytic reactions, the Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst with large and accessible pore surface area exhibited excellent catalytic activity as compared to other noble metal supported catalysts. The Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst could also be easily and conveniently recovered from the reaction mixture by using an external magnet, attributed to its magnetism, thus preventing the catalyst loss. Moreover, it could also be reused for at least six times without significant decrease in the catalytic activity, indicating its excellent reusability and stability. This study provides a useful platform and a new perspective for fabricating mesoporous MnO2 microspheres based noble metals modified catalysts for environmental catalysis.Download full-size imageIn this paper, we successfully prepared magnetic SiO2@Fe3O4@m-MnO2 microspheres with uniform morphology and mesoporous MnO2 shell. The prepared material was used as a catalyst support for fabricating the Pd(6%)/SiO2@Fe3O4@m-MnO2 nanocatalyst which exhibited excellent catalytic activity and easy recyclability in the environmental catalysis.

In this work, we described a methodology to immobilize Salen Pd (II) complex on the surface of magnetite nanoparticles. The palladium catalyst exhibited efficient catalytic activity in coupling reactions with aryl iodides or bromides and phenylboronic acid at 100 °C for 1–3 h under DMF/H2O. Furthermore, the catalyst could be magnetically isolated with a permanent magnet and the yields achieved above 85% after reused at least 5 times.Download full-size imageHighlights► The catalyst was prepared by immobilization of Salen Pd (II) complex on Fe3O4@SiO2. ► The catalyst exhibited efficient catalytic activity for Suzuki reaction in DMF/H2O. ► The catalyst could be magnetically isolated with a permanent magnet. ► The yields achieved above 85% after the catalyst was reused at least 5 times.

Recently, it has become imperative to design non-precious-metal-based nanocatalysts with high catalytic efficiency for the hydrogenation of nitroarenes to the corresponding aromatic amines under mild reaction conditions. In this study, γ-Fe2O3-nanoparticle-supported hollow mesoporous carbon microsphere (h-MCM) nanocatalysts (γ-Fe2O3/h-MCM) were prepared, and their catalytic performance for the hydrogenation of nitroarenes was investigated. Here, h-MCM prepared by the co-sol–emulsion-gel method exhibited a mesoporous hollow structure, high surface area, and accessible interior space as well as a graphitic carbon framework; thus, aromatic compounds can sufficiently come into contact with the active sites, as well as enhance the mass transfer effect. N2H4·H2O used herein as the reducing agent only generated N2 and H2O as harmless by-products. γ-Fe2O3/h-MCM was obtained by the calcination of Fe(NO3)3-absorbed h-MCM under an inert atmosphere. From transmission electron microscopy results, the annealing temperature significantly affected the γ-Fe2O3 particle size, and in turn catalytic activity: the γ-Fe2O3/h-MCM nanocatalyst annealed at 500 °C for 15 min (20%-γ-Fe2O3/h-MCM-500-15) exhibited high catalytic activity. By the use of 20%-γ-Fe2O3/h-MCM-500-15 as the optimal catalyst, all nitroarenes investigated for hydrogenation exhibited high conversion, with a 100% selectivity for aniline, indicating the excellent selectivity of γ-Fe2O3-based catalysts. In addition, the catalyst can be easily recovered with an external magnetic field and reused at least five times without obvious decrease in catalytic activity. This study provides a useful platform based on a cost-effective, magnetically recyclable γ-Fe2O3-based nanocatalyst for the highly efficient hydrogenation of nitroarenes.

In this study, a novel core–shell magnetic fibrous nanocatalyst, Pd/Fe3O4@SiO2@KCC-1 with easily accessible active sites and a convenient recovery by applying an external magnetic field, was successfully developed. Fe3O4@SiO2@KCC-1 was functionalized with amino groups which act as robust anchors so that the palladium nanoparticles (Pd NPs) with an average diameter of about 4 nm were well-dispersed on the fibers of Fe3O4@SiO2@KCC-1 without obvious aggregation. The synthesized Pd/Fe3O4@SiO2@KCC-1 nanocatalyst exhibited excellent catalytic activity in the reduction of 4-nitrophenol by sodium borohydride, and the Suzuki cross coupling reactions of aryl chlorides with aryl boronic acids due to the easy accessibility of the active sites. Furthermore, the Pd/Fe3O4@SiO2@KCC-1 nanocatalyst was conveniently recovered by a magnet and could be reused for at least five cycles without significant loss in activity, thus confirming its good stability. Therefore, the abovementioned approach based on core–shell magnetic fibrous Fe3O4@SiO2@KCC-1 provided a useful platform for the fabrication of Pd NPs based catalysts with easy accessibility, superior activity and convenient recovery.

The development of low cost noble metal nanocatalysts with high activity and selectivity, high catalytic performance, convenient separation, and reusability is a significant challenge. Herein, the magnetic porous carbon (MPC) composite synthesized from metal organic framework (MOF) was used as a catalyst support to fabricate gold (Au) and palladium (Pd) nanoparticle (NP) based nanocatalysts. The MPC not only provided a large surface area and mesopores on which the active centers (Au and Pd NPs) were finely dispersed, but also exhibited superparamagnetic behaviour that enabled the magnetic separation and convenient recovery of the nanocatalysts from the reaction mixture. Thus, the nanocatalysts were repeatedly used without loss of catalytic efficiency. Both the Au/MPC and Pd/MPC nanocatalysts showed excellent catalytic activity for the reduction of 4-nitrophenol. Moreover, the Pd/MPC nanocatalyst exhibited higher efficiency toward hydrodechlorination of 4-chlorophenol compared to the other reported catalysts. This study indicated that the noble metal NPs (NMNPs) supported on MOF-derived MPC materials could act as promising catalysts exhibiting potential applications in numerous NMNP based catalytic reactions.