Double shelled titanium dioxide@mesoporous organosilica nanotube as an amphiphilic photoactive nanoreactor for efficient photocatalytic oxidation of styrene

In this work, we have proposed a strategy to fabricate double-shell nanotubes as amphiphilic photoactive nanoreactors (HTTBPC) through the ordered hybridization of mesoporous organosilicon (PMO) and titanium dioxide (TiO2) nanotubes. Unlike the previous rough composite, the heterogeneous structure established between cobalt-porphyrin functionalized PMO and conventional TiO2 has a staggered matching band gap, which makes it have excellent light harvesting and high carrier separation ability. This is still unexplored. Interestingly, the prepared photocatalysts exhibited superior activity (99%) and benzaldehyde selectivity (94%) in the oxidation of styrene in water at room temperature, which was 3.8 and 2.8 times higher than that of TiO2 nanotubes and PMO functionalized with cobalt porphyrin, respectively. It was demonstrated that the strong interaction between cobalt porphyrin PMO and TiO2 improved the separation of photogenerated carriers and the amphiphilic properties of mesoporous organosilica boosted the adsorption of substrate molecules in water, contributing to the significantly enhanced photocatalytic activity. This work provides a design of high-performance photocatalysts for alkene oxidation under green conditions.

Polymer-capped gold nanoparticles as nanozymes with improved catalytic activity for the monitoring of serum ciprofloxacin

More recently, gold nanoparticle (AuNP)-based nanozymes have become one of the burgeoning research hot topics. However, few studies have focused on these AuNP-nanozymes with polymers as ligands. A significant challenge is to reveal their catalytic mechanism and to improve their catalytic activity by changing the structures of the polymers. In this study, polyacrylamide (PAM) with different chain lengths was synthesized and used as the ligand to prepare PAM@AuNPs. The resultant nanozymes exhibited good peroxidase-like activity for catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H₂O₂). In particular, due to the electrostatic interaction between the negatively charged PAM@AuNPs and the positively charged drug, the addition of ciprofloxacin in the oxidation system induced the aggregation of PAM@AuNPs and produced more amount of reactive oxygen species, which greatly promoted the catalytic activity of PAM@AuNPs. Inspired by the attractive property, a highly selective and sensitive colorimetric assay for the monitoring of ciprofloxacin was created. A good linear relationship between the UV-Vis absorption intensity of PAM@AuNPs-TMB-H₂O₂ at 650 nm wavelength and the ciprofloxacin concentration was observed ranging from 1.0 μM to 12.0 μM (R² = 0.998), providing the detection limit of 0.5 μM. The ciprofloxacin metabolism was further studied in rats. It reveals great potential of polymer protected AuNP-nanozymes in practical drug analysis.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Comparative toxicity of rod-shaped nano-CeO2 and nano-CePO4 to lettuce

The influence of morphology on the biological effects of nanomaterials (NMs) has not been well understood. In the present study, we compared the phytotoxicity of rod-shaped nano-cerium dioxide (R-CeO2) and nano-cerium phosphate (R-CePO4) to lettuce plants. The results showed that R-CeO2 significantly inhibited the root elongation of lettuce, induced oxidative damages, and caused cell death, while R-CePO4 was nontoxic to lettuce. The different distribution and speciation of Ce in plant tissues were determined by transmission electron microscopy (TEM) and X-ray absorption near edge spectroscopy (XANES) combined with linear combination fitting (LCF). The results showed that in the R-CeO2 group, part of Ce was transformed from Ce(IV) to Ce(III), while only Ce(III) was present in the R-CePO4 group. When interacting with plants, R-CeO2 is easier to be dissolved and transformed than R-CePO4, which might be the reason for their different phytotoxicity. Although both are Ce-based NMs and have the same morphology, the toxicity of R-CeO2 seems to come from the released Ce3+ ions rather than its shape. This research emphasizes the importance of chemical composition and reactivity of NMs to their toxicological effects.

Catalytic C-H aerobic and oxidant-induced oxidation of alkylbenzenes (including toluene derivatives) over VO2+ immobilized on core-shell Fe3O4@SiO2 at room temperature in water

Direct C–H bond oxidation of organic materials, and producing the necessary oxygenated compounds under mild conditions, has attracted increasing interest. The selective oxidation of various alkylbenzenes was carried out by means of a new catalyst containing VO²⁺ species supported on silica-coated Fe₃O₄ nanoparticles using t-butyl hydroperoxide as an oxidant at room temperature in H₂O or solvent-free media. The chemical and structural characterization of the catalyst using several methods such as FTIR spectroscopy, XRD, FETEM, FESEM, SAED, EDX and XPS showed that VO²⁺ is covalently bonded to the silica surface. High selectivity and excellent conversion of various toluene derivatives, with less reactive aliphatic (sp³) C–H bonds, to related benzoic acids were quite noticeable. The aerobic oxygenation reaction of these alkylbenzenes was studied under the same conditions. All the results accompanied by sustainability of the inexpensive and simple magnetically separable heterogeneous catalyst proved the important criteria for commercial applications.

A highly efficient, recoverable, sustainable, economic and eco-friendly catalyst containing VO²⁺ species supported on SiO₂@Fe₃O₄ nanoparticles for selective oxidation of alkylbenzenes using TBHP or O₂ at room temperature in H₂O or solvent-free media.

Selective Liquid-Phase Oxidation of Toluene with Molecular Oxygen Catalyzed by Mn3O4 Nanoparticles Immobilized on CNTs under Solvent-Free Conditions

The catalytic performance of Mn3O4 supported on carbon nanotubes (CNTs) in the liquid-phase oxidation of toluene to benzyl alcohol and benzaldehyde was studied. The supported catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption isotherms and ICP-MS. The results demonstrate that Mn3O4 nanoparticles loaded on CNTs performed better compared with pristine Mn3O4 or CNTs. The main reason for the increased catalytic activity is the dispersion and loading of Mn3O4 in CNTs. By optimizing the reaction temperature, reaction time, catalyst quality, oxygen flow rate and initiator dosage, the optimum reaction conditions were obtained. Using tert-butyl hydroperoxide (TBHP) as the initiator and oxygen as the oxidant, the toluene conversion rate was as high as 24.63%, and benzyl alcohol and benzaldehyde selectivity was 90.49%. The good stability of the catalyst was confirmed by repeating the experiment for four cycles and observing no significant changes in its performance.

Sustainable Oxidation of Cyclohexane and Toluene in the Presence of Affordable Catalysts: Impact of the Tandem of Promoter/Oxidant on Process Efficiency

The oxygenation of cyclohexane and toluene by O₂ and H₂O₂ catalyzed by VO(acac)₂ and Co(acac)₂ was studied at 40-100 °C and 1-10 atm. Upon such conditions, the process can be remarkably (30× times) enhanced by the minute (6-15 mM) additives of oxalic acid (OxalH) or N-hydroxyphthalimide (NHPI). The revealed effect of OxalH on H₂O₂-piloted oxidation is closely associated with the nature of the catalyst cation and boosted by VO(acac)₂. Whereas the effectiveness of Co(acac)₂-based systems was curbed by the addition of OxalH and remained much below the one displayed with the previous system. The observed conspicuous difference in activity was attributed to the substantially higher solubility of in situ formed VO(IV)oxalate compared to that of Co(II)oxalate. The exploration of H₂O₂ for the NHPI-promoted process leads to the decisively lower (5-7 times) yield in comparison to the O₂-driven reaction. Similarly, for the O₂-operated protocol, the yield cannot be improved by addition of OxalH either to VO(acac)₂ + NHPI or to Co(acac)₂ + NHPI mixture. By contrast, the combination of NHPI with VO(acac)₂ or Co(acac)₂ and particularly with the above two mixtures in O₂-piloted oxidation enhances the yield of the aimed products 3-6 times regardless of the substrate used. The revealed significant synergetic effect of the cobalt + vanadyl bicomponent catalyst was due to the participation of each of its moiety in the different stages of the process mechanism. Only benzyl alcohol and benzaldehyde were identified in VO(acac)₂- or Co(acac)₂-catalyzed toluene oxidation, while cyclohexane oxidation yields cyclohexylhydroperoxide in line with cyclohexanol and cyclohexanone. The putative mechanism of investigated processes is highlighted and discussed.

Fabricating Surface-Functionalized CsPbBr3/Cs4PbBr6 Nanosheets for Visible-Light Photocatalytic Oxidation of Styrene

The halide perovskite (PVSK) material, an excellent light absorber with fast carrier kinetics, has received increased attention as a potential photocatalyst for organic synthesis. Herein, we report a straightforward synthesis of chemically modified halide perovskite and its application as an efficient photocatalyst to convert styrene into benzaldehyde. A simple method is employed to synthesize the chemically modified CsPbBr₃/Cs₄PbBr₆ nanosheets by using ZrCl₄ to simultaneously achieve the Cl doping and the surface modification with Zr species. The photocatalytic oxidation rate of styrene to benzaldehyde catalyzed by surface-modified CsPbBr₃/Cs₄PbBr₆ nanosheets under visible light can reach 1,098 μmol g⁻¹ h⁻¹, 2.9 times higher than that of pristine CsPbBr₃/Cs₄PbBr₆ nanosheets (372 μmol g⁻¹ h⁻¹). The enhanced photocatalytic performance may originate from the modified band structure induced by the synergistic effect of Cl doping and surface modification, whereby the same methodology can be applied to MAPbBr₃. This work demonstrates the surface modification of PVSK materials and their potential as efficient photocatalyst toward organic synthesis.

Influence of Surface Charge on the Phytotoxicity, Transformation, and Translocation of CeO2 Nanoparticles in Cucumber Plants

The physiochemical properties of nanoparticles (NPs), including surface charge, will affect their uptake, transformation, translocation, and final fate in the environment. In this study, we compared the phytoxoxicity and transport behaviors of nano CeO₂ (nCeO₂) functionalized with positively charged (Cs-nCeO₂) and negatively charged (PAA-nCeO₂) coatings. Cucumber seedlings were hydroponically exposed to 0-1000 mg/L of Cs-nCeO₂ and PAA-nCeO₂ for 14 days and the contents, distribution, translocation, and transformation of Ce in plants were analyzed using inductively coupled plasma mass spectrometry, micro X-ray fluorescence (μ-XRF), and X-ray absorption near-edge spectroscopy (XANES), respectively. Results showed that the seedling growth and Ce contents in plant tissues were functions of exposure concentrations and surface charge. Cs-nCeO₂ was adsorbed strongly on a negatively charged root surface, which led to significantly higher Ce contents in the roots and lower translocation factors of Ce from the roots to shoots in Cs-nCeO₂ group than in PAA-nCeO₂ group. The results of μ-XRF showed that Ce elements were mainly accumulated at the root tips and lateral roots, as well as in the veins and at the edge of leaves. XANES results revealed that the proportion of Ce(III) was comparable in the plant tissues of the two groups. We speculated that Cs-nCeO₂ and PAA-nCeO₂ were partially dissolved under the effect of root exudates, releasing Ce³⁺ ions as a result. Then, the Ce³⁺ ions were transported upward in the form of Ce(III) complexes along the vascular bundles and eventually accumulated in the veins. The other portion of Cs-nCeO₂ and PAA-nCeO₂ entered the roots through the gap of a Casparian strip at root tips/lateral roots and was transported upward as intact NPs and finally accumulated at the edge of the blade. This study will greatly advance our information on how the properties of NPs influence their phytotoxicity, uptake, and subsequent trophic transfer in terrestrial food webs.

Selective oxidation of glycerol on morphology controlled ceria nanomaterials

It is reported, for the first time, that morphology controlled ceria without any addition of other metal exhibits catalytic activity for selective oxidation of glycerol. Moreover, development of {111} nanofacets plays an important role in both activity and selectivity.

Solvent-free selective oxidation of toluene over metal-doped MCM-22

The synthesis of MCM-22, subsequent metal doping, and physicochemical characterization of the products are reported. The solvent-free catalytic oxidation of toluene using hydrogen peroxide is explored, and the reaction parameters are optimized. A possible reaction mechanism is also described.

A hexagonal Ni6 cluster protected by 2-phenylethanethiol for catalytic conversion of toluene to benzaldehyde

A hexagonal Ni₆ cluster protected by 2-phenylethanethiol was synthesized and achieved a high performance for catalytic conversion of toluene to benzaldehyde.

Interfacial Modification of Photoanode|Electrolyte Interface Using Oleic Acid Enhancing the Efficiency of Dye-Sensitized Solar Cells

Dye-sensitized solar cells (DSSCs) are useful devices in converting renewable solar energy into electrical energy. In DSSCs, the triiodide reduction at the surface of TiO₂ is one of the detrimental processes that limit the realization of high efficiencies of the device. To alleviate the active sites available on the semiconductor surface for this detrimental process, the interfacial modification of the dye-adsorbed TiO₂|electrolyte interface has been attempted by coadsorption of oleic acid (OA) over the TiO₂ surface. Thus, the modified cell exhibited a higher efficiency (η) of 12.9% under one sun illumination when compared with that of the unmodified cell (η = 11.1%). To provide an insight into the OA anchoring and dynamics of electron transport at the photoanode|electrolyte interface, molecular spectroscopic and electrochemical impedance spectroscopic analyses were carried out. A red shift in the optical absorption spectrum was observed after the addition of OA to dye-adsorbed TiO₂. The binding of OA to TiO₂ surface was found to be through bridging bidentate type. Mott-Schottky analyses of the DSSCs under dark conditions were made to probe the shift in the Fermi level of TiO₂ upon OA modification. In addition, the Förster resonance energy transfer (FRET) has been found between OA and N719 dye. Thus, the red shift in the optical absorption, enhanced electron-transfer kinetics, and FRET contributes to the observed enhancement in the efficiency of the device containing OA-modified photoanode.

Highly selective oxidation of styrene to benzaldehyde over a tailor-made cobalt oxide encapsulated zeolite catalyst

A tailor-made catalyst with cobalt oxide particles encapsulated into ZSM-5 zeolites (Co₃O₄@HZSM-5) was prepared via a hydrothermal method with the conventional impregnated Co₃O₄/SiO₂ catalyst as the precursor and Si source. Various characterization results show that the Co₃O₄@HZSM-5 catalyst has well-organized structure with Co₃O₄ particles compatibly encapsulated in the zeolite crystals. The Co₃O₄@HZSM-5 catalyst was employed as an efficient catalyst for the selective oxidation of styrene to benzaldehyde with hydrogen peroxide as a green and economic oxidant. The effect of various reaction conditions including reaction time, reaction temperature, different kinds of solvents, styrene/H₂O₂ molar ratio and catalyst dosage on the catalytic performance were systematically investigated. Under the optimized reaction condition, the yield of benzaldehyde can achieve 78.9% with 96.8% styrene conversion and 81.5% benzaldehyde selectivity. Such an excellent catalytic performance can be attributed to the synergistic effect between the confined reaction environment and the proper acidic property. In addition, the reaction mechanism with Co₃O₄@HZSM-5 as the catalyst for the selective oxidation of styrene to benzaldehyde was reasonably proposed.

Polyoxometalate-based Gemini ionic catalysts for selective oxidation of benzyl alcohol with hydrogen peroxide in water

Polyoxometalate-based Gemini ionic hybrids with inherent phase transfer capability are highly efficient and recyclable catalysts in the selective oxidation of alcohols with H₂O₂ in water.

Reaction Sensitivity of Ceria Morphology Effect on Ni/CeO2 Catalysis in Propane Oxidation Reactions

CeO₂ nanocubes (c-CeO₂), nanoparticles (p-CeO₂), and nanorods calcined at 500 °C (r-CeO₂-500) and 700 °C (r-CeO₂-700) were used as supports to synthesize a series of Ni/CeO₂ catalysts for the propane combustion and oxidative dehydrogenation of propane (ODHP) reactions. The Ni-CeO₂ interaction greatly promotes the reducibility of CeO₂, but CeO₂ morphology-dependent Ni-CeO₂ interaction was observed to form different speciation of Ni species (Ni²⁺ dissolved in CeO₂, highly dispersive NiO, NiO aggregate) and oxygen species (strongly activated oxygen species, medially activated oxygen species, weakly activated oxygen species) in various Ni/CeO₂ catalysts. Ni-CeO₂ interaction is stronger in Ni/c-CeO₂ catalysts than in other Ni/CeO₂ catalysts. Different morphology-dependences of Ni/CeO₂ catalysts in propane combustion and ODHP reactions were observed. The Ni/r-CeO₂-500 catalyst with the largest strongly activated oxygen species is most catalytic active in the propane combustion reaction while the Ni/c-CeO₂ catalyst with the largest amount of weakly activated oxygen species exhibits the best catalytic performance in the ODHP reaction. Thus, the CeO₂ morphology engineering strategy is effective in finely tuning the metal-CeO₂ interaction and the reactivity of oxygen species to meet the requirements of different types of catalytic oxidation reactions.

Comparison of two fabricated aptasensors based on modified carbon paste/oleic acid and magnetic bar carbon paste/Fe3O4@oleic acid nanoparticle electrodes for tetracycline detection

In this research, we have improved two aptasensors based on a modified carbon paste electrode (CPE) with oleic acid (OA), and a magnetic bar carbon paste electrode (MBCPE) with Fe3O4 magnetic nanoparticles and oleic acid (OA). After the immobilization process of anti-TET at the electrode surfaces, the aptasensors were named CPE/OA/anti-TET and MBCPE/Fe3O4NPs/OA/anti-TET respectively. In this paper, the detection of tetracycline is compared using CPE/OA/anti-TET and MBCPE/Fe3O4NPs/OA/anti-TET aptasensors. These modified electrodes were characterized by infrared spectroscopy (IR), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), UV-vis spectroscopy, and voltammetric methods. The linear range and the detection limit for TET with the CPE/OA/anti-TET aptasensor were found to be 1.0×10(-12)-1.0×10(-7)M and 3.0×10(-13)M respectively by EIS method. The linear range and the detection limit for TET with the CPE/OA/anti-TET aptasensor were found to be 1.0×10(-10)-1.0×10(-7)M with a limit of detection of 2.9×10(-11)M using differential pulse voltammetry (DPV) technique. The MBCPE/Fe3O4NPs/OA/anti-TET aptasensor was used for determination of TET, and a liner range of 1.0×10(-14)-1.0×10(-6)M with a detection limit of 3.8×10(-15)M was obtained by EIS method. Also, the linear range and detection limit of 1.0×10(-12)-1.0×10(-6)M and 3.1×10(-13)M respectively, were obtained for MBCPE/Fe3O4NPs/OA/anti-TET aptasensor using DPV. The proposed aptasensors were applied for determination of tetracycline in some real samples such as drug, milk, honey and blood serum samples.

The cascade synthesis of α,β-unsaturated ketones via oxidative C–C coupling of ketones and primary alcohols over a ceria catalyst

We herein report the oxidative C–C coupling of ketones and primary alcohols to produce α,β-unsaturated ketones in the absence of base additives.

Synthesis, characterization and optical properties of ligand-protected indium nanoparticles

Small ligand-protected indium nanoparticles exhibit reverse plasmonics behavior in the ultraviolet region.

Hollow iron oxide nanoshells are active and selective catalysts for the partial oxidation of styrene with molecular oxygen

Well defined hollow iron oxide nanoshells are active, selective and recyclable catalysts for the oxidation of styrene into benzaldehyde using difficult-to-activate molecular oxygen as the sole oxidant.