Direct electrodeposition of cationic pillar[6]arene-modified graphene oxide composite films and their host–guest inclusions for enhanced electrochemical performance

In the present work, electrochemically reduced graphene oxide-cationic pillar[6]arene (ErGO-CP6) composite films on glassy carbon electrodes (GCEs) were prepared directly from graphene oxide-cationic pillar[6]arene (GO-CP6) dispersions by a facile one-step pulsed electrodeposition technique. The preparation of GO-CP6 and its subsequent electrochemical reduction were confirmed by Fourier transform infrared (FTIR) spectroscopy, UV-vis spectroscopy (UV-vis), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), zeta potential, Raman spectroscopy, and scanning electron microscopy (SEM). SEM result reveals that ErGO-CP6 could form a homogeneous film when GO-CP6 was electrodeposited on the surface of a GCE. Furthermore, Raman and XPS results confirm the removal of oxygen-containing functional groups present on the GO-CP6 surface after electrochemical reduction. Electrochemical results reveal that ErGO-CP6 films could show much higher electrochemical response to theophylline (TP), ascorbic acid (AA), acetaminophen (APAP), and folic acid (FA) than unmodified ErGO films and bare GCE, which is considered to be the synergistic effect of the graphene (excellent electrical properties and large surface area) and CP6 molecules (high inclusion complexation and enrichment capability).

Cationic pillar[6]arene functionalized graphene films with enhanced host–guest electrochemical recognition performance were fabricated directly from GO-CP6 dispersions by a one-step pulsed electrodeposition technique.     

Hierarchical self-assembly of discrete bis-[2]pseudorotaxane metallacycle with bis-pillar[5]arene via host–guest interactions and their redox-responsive behaviors

A discrete rhomboidal metallacycle R functionalized with bis-[2]pseudorotaxane of [Cu(phenanthroline)₂]⁺ derivatives was successfully synthesized via coordination-driven self-assembly. Furthermore, the host–guest complexation of such a bis-[2]pseudorotaxane metallacycle with a bis-pillar[5]arene (bisP5) allowed for the formation of a new family of cross-linked supramolecular polymers R⊃(bisP5)₂, which displayed interesting redox-responsive properties. By taking advantage of the substantial structural differences between the coordination geometries of [Cu(phenanthroline)₂]⁺ and [Cu(phenanthroline)₂]²⁺, the weight-average diffusion coefficients D of the supramolecular polymer were adjusted through changing the redox state of the Cu(i)/Cu(ii) complexes.

We presented a new family of supramolecular polymers cross-linked by bis-[2]pseudorotaxane metallacycles with interesting redox-responsive behavior.     

Ultrasensitive electrochemical detection of methyl parathion pesticide based on cationic water-soluble pillar[5]arene and reduced graphene nanocomposite

We report a rapid, sensitive and selective electrochemical sensor based on pillar[5]arene (CP5) reduced graphene (rGO) nanohybrid-modified glassy carbon electrode CP5-rGO/GCE for the trace detection of methyl parathion (MP) by differential pulse voltammetry (DPV) for the first time. Compared to beta-cyclodextrin (β-CD)-functionalized reduced graphene (rGO)-modified GCE β-CD-rGO/GCE, the proposed CP5-rGO/GCE sensor exhibits excellent electrochemical catalytic activity, rapid response, high sensitivity, good reproducibility and anti-interference ability towards MP. The recognition mechanism of β-CD/MP and CP5/MP was studied by ¹H NMR. The results indicate a higher supramolecular recognition capability between CP5 and MP compared to that between β-CD and MP. The β-CD-rGO and CP5-rGO nano-composites were prepared via a wet chemistry approach. The resulting nano-composites have been characterized by thermogravimetric analysis (TGA), fourier transform infrared spectrometry (FTIR), charge transfer resistance (R_ct) and zeta potential. The CP5-rGO/GCE combines the merits of CP5 and rGO, and is used for quantitative detection of MP. It has a low detection limit of 0.0003 μM (S/N = 3) and a linear response range of 0.001–150 μM for MP. This method has been used to detect MP in soil and waste water samples with satisfactory results. This study provides a promising electrochemical sensing platform and is a promising tool for the rapid, facile and sensitive analysis of MP.

A promising electrochemical sensing platform for the detection of methyl parathion based on cationic water-soluble pillar[5]arene reduced graphene nanocomposite.     

A combined crystallography and DFT study on ring-shaped Cucurbit[n]urils: structures,surface character,and host–guest recognition

A combined crystallography and DFT study of cucurbit[n]urils (n = 5–8, 10) was carried out, and PBE0 was certified to be the most rational density functional method for optimization task. Steric hindrance and electronic effect of the hindered lone pair electrons in cucurbit[n]urils were qualitatively measured by bond order analysis, lone pair electron (LP) visualization and electrostatic potential (ESP) study. Together with energy decomposition analysis of some selected host–guest systems, we quantitatively verified the effect of size/cavity and noncovalent interaction in host–guest recognition. This solid study revealed that lone pairs electrons affect not only on host–guest identification mode but also on geometry stability, which pave the avenue for further sophisticated applications.

A combined crystallography and DFT study of CB[n]s (n = 5–8, 10) was carried out. Through wavefunction analysis, how the hindered lone pair electrons affect on structures, electrostatics potential distribution and host–guest recognition were disclosed.     

Correction: Water-floating nanohybrid films of layered titanate–graphene for sanitization of algae without secondary pollution

Correction for ‘Water-floating nanohybrid films of layered titanate–graphene for sanitization of algae without secondary pollution’ by In Young Kim et al., RSC Adv., 2016, 6, 98528–98535.

In the published paper, the affiliations of Eui-Ho Hwang and Woo-Bin Jin were wrongly designated, and the corrected version is shown below.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

A hybrid composite of H2V3O8 and graphene for aqueous lithium-ion batteries with enhanced electrochemical performance

Aqueous rechargeable lithium-ion batteries (ARLBs) are regarded as a competitive challenger for large-scale energy storage systems because of their high safety, modest cost, and green nature. A kind of modified composite material composed of H₂V₃O₈ nanorods and graphene sheets (HVO/G) has been effectively made by a one-step hydrothermal method and following calcination at 523 K. XRD, SEM, TEM, and TG are used to determine the phase structures and morphologies of the composite materials. Owing to the advantage of the layered structure of H₂V₃O₈ nanorods, the excellent conductivity of the graphene sheets, and the 3D network structure of the modified composite, the ARLBs with HVO/G can deliver an adequate specific capacity of 271 mA h g⁻¹ at 200 mA g⁻¹ and have a retention rate of 73.4% after 50 cycles. The average discharge capacity of ARLB with HVO/G as anode has a considerable improvement over that of HVO/CNTs and HVO, whatever the current rate used. Moreover, we find that the diffusion coefficient of lithium-ion increases by an order of magnitude through the theoretical calculation for HVO/G ARLB. The new ARLB with HVO/G electrode is a potential energy storage system with great advantages, such as simple preparation, easy assembly process, excellent safety and low-cost environmental protection.

Aqueous rechargeable lithium-ion batteries (ARLBs) are regarded as a competitive challenger for large-scale energy storage systems because of their high safety, modest cost, and green nature.     

Host–guest modes and supramolecular frameworks of complexes of tetramethyl cucurbit[6]uril with 4-chloroaniline and 4,4′-diaminostilbene

Since the first reportal on decamethylcucurbit[5]uril (Me₁₀Q[5]) in 1992, substituted cucurbit[n]urils have attracted considerable research interest. In this study, the host–guest modes between the tetramethyl cucurbit[6]uril (TMeQ[6]) as a host and 4-chloroaniline and 4,4′-diaminostilbene (G1 and G2) as guests were investigated by single-crystal X-ray diffraction, NMR, ITC, UV-Vis spectrum, and MALDI-TOF mass spectrometry analyses. The experimental results showed that TMeQ[6] formed a 1 : 1 inclusion compound with G1, and the carbonyl portal of TMeQ[6] formed a 1 : 1 self-assembly with G2. Further, multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C–H⋯π interactions, ion–dipole interactions, and dipole–dipole interactions).

Two TMeQ[6]-based multi-dimensional supramolecular frameworks were formed driven by weak interaction forces in the system (hydrogen bonding, C–H... π interactions, ion–dipole interactions, and dipole–dipole interactions).     

Correction: Utilizing FBR to produce olefins from CO reduction using Fe–Mn nanoparticles on reduced graphene oxide catalysts and comparing the performance with SBR

Correction for ‘Utilizing FBR to produce olefins from CO reduction using Fe–Mn nanoparticles on reduced graphene oxide catalysts and comparing the performance with SBR’ by AL-Hassan Nasser et al., RSC Adv., 2018, 8, 42415–42423.

The authors regret that the original author list was incorrect. The correct author list is as shown above.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Graphdiyne bearing pillar[5]arene-reduced Au nanoparticles for enhanced catalytic performance towards the reduction of 4-nitrophenol and methylene blue

Graphdiyne (GD), a novel two dimensional (2D) carbon material, has earned a lot of attention in recent years. Constructing a novel hybrid nanomaterial based on GD, macrocyclic host and Au nanoparticles is an effective strategy for heterogeneous catalysis applications. While tremendous advancements in the preparation of two dimensional (2D) materials anchoring Au nanoparticles have been made, it is an urgent requirement to explore a green, efficient and facile approach for obtaining small-sized Au nanoparticles. The use of the 2D material graphdiyne (GD) presents more-promising candidates for constructing excellent sites for loading metal nanoparticles. In this study, a novel 2D heterogeneous hybrid nanomaterial (P5A-Au-GD) based on GD and pillar[5]arene (P5A)-reduced Au nanoparticles (P5A-Au) was successfully prepared. In this strategy, the P5A can reduce HAuCl₄ with the aid of NaOH in the dispersion of GD. Accordingly, the generated P5A-Au can immediately interact with GD to form the P5A-Au-GD hybrid nanomaterial without any harsh reduced materials or other energies. The Au nanoparticles with average diameter of 2–3 nm are homogeneously dispersed on the surface of GD. The heterogeneous 2D catalyst of P5A-Au-GD shows high catalytic performances in the reduction of 4-nitrophenol and methylene blue by comparing commercial Pd/C catalyst. Meanwhile, the unique 2D heterogeneous hybrid material P5A-Au-GD exhibits durable recyclability and stability during the catalytic reaction. Considering the outstanding merits of the heterogeneous 2D catalyst of P5A-Au-GD as well as the simple and green preparation, this study might not only present enormous opportunities for the stabilized, high-performance and sustainable catalysts but also be applied in other frontier studies of sustainable functionalized nanocomposites and advanced materials.

Application of a novel 2D heterogeneous hybrid nanomaterial based on graphdiyne and pillar[5]arene-reduced Au nanoparticles in catalyzing the reduction of 4-nitrophenol and methylene blue.     

An ionic liquid–molecularly imprinted composite based on graphene oxide for the specific recognition and extraction of cancer antigen 153

Molecularly imprinted polymers with graphene oxide (GO) as a carrier (GMIPs) were synthesized to selectively recognize and capture cancer antigen 153 (CA153). The results show that the MIP has good selectivity and adsorption for CA153, and has strong anti-interference ability. Molecularly imprinted solid phase extraction (MISPE) combined with ultra performance liquid chromatography (UPLC) for the specific adsorption of CA153 was also established, and showed great potential for the analysis of CA153 in clinics in the future.

In this research, we used GO as the support material, IL as the stabilizer, CA153 as the template and DA as the functional monomer for the preparation of GMIPs. The GMIP was successfully used as an enrichment agent for the selective enrichment of CA153.     

Photoelectric and flexible poly(styrene-b-ethylene/butylene-b-styrene)-zinc porphyrin–graphene hybrid composite: synthesis,performance, and mechanism

Stretchable and flexible photoelectric materials are highly desirable for the development of artificial intelligence products. However, it remains a challenge to fabricate a stable, processable, and cost-efficient material with both high photoelectric sensitivity and remarkable deformability. Herein, a new kind of photoelectric sensitive, highly stretchable and environmentally adaptive materials was developed through in situ synthesis and π–π conjugation design. Specifically, a photoelectric elastomer zinc porphyrin SEBS(Zn-PorSEBS) was synthesized by introducing porphyrin to SEBS chain via a one-pot method. Then, graphene/zinc porphyrin SEBS (G/Zn-PorSEBS) composites were obtained by combing the elastomer with graphene sheets through solution blending. Notably, the resultant flexible composites were capable of capturing light changes with illumination on or off, and the maximum photocurrent density reached 0.13 μA cm⁻². Moreover, the photoelectric composites exhibited a dramatic elongation (more than 1000%) and an excellent tensile strength about 20 MPa. This proposed strategy represents a general approach to manufacture photoelectric and flexible materials.

Stretchable and flexible photoelectric materials are highly desirable for the development of artificial intelligence products.     

In situ generation of exfoliated graphene layers on recycled graphite rods for enhanced capacitive performance of Ni–Co binary hydroxide

A functionalized exfoliated graphite rod (FEGR), with a high surface area, is produced for use as a promising substrate for supercapacitors, via controlled oxidative treatment of a recycled graphite rod of exhausted zinc–carbon batteries. SEM, EDX, XPS, FT-IR, Raman, and contact angle measurements are carried out to disclose the surface characteristics of the FEGR. The surface of the FEGR is characterized by in situ generated grooves, together with graphene layers which are directly attached to the underlying graphite base. The FEGR electrodes enhance the capacitive performance of Ni(OH)₂ and binary Ni–Co(OH)₂. The Ni–Co(OH)₂/FEGR electrode displays a superb specific capacity value (2552.6 C g⁻¹) at a current density of 5 A g⁻¹ and this value is retained to 70.8% at a high current density of 50 A g⁻¹ indicating the outstanding rate performance of this electrode material. This enhanced behavior is attributed to the facile interaction of electrolyte species, even at high current density, with the active sites of the redox catalyst layer (distributed over a larger fraction of the underlying substrate with enhanced hydrophilicity). Moreover, the excellent electrical conductivity of the in situ surface generated graphene layers is another promoting factor.

A functionalized exfoliated graphite rod (FEGR), with a high surface area, is produced for use as a promising substrate for supercapacitors, via controlled oxidative treatment of a recycled graphite rod of exhausted zinc–carbon batteries.     

Graphene oxide–metal oxide nanocomposites: fabrication,characterization and removal of cationic rhodamine B dye

The fabrication and characterization of graphene oxide (GO) nanosheets and their reaction with Fe₃O₄ and ZrO₂ metal oxides to form two nanocomposites, namely graphene oxide–iron oxide (GO–Fe₃O₄) and graphene oxide–iron oxide–zirconium oxide (GO–Fe₃O₄@ZrO₂), have been examined. The fabricated nanocomposites were examined using different techniques, e.g.transmission electron microscopy, X-ray diffraction, zeta potential measurement and Fourier transform infrared spectroscopy. Compared to GO, the newly fabricated GO–Fe₃O₄ and GO–Fe₃O₄@ZrO₂ nanocomposites have the advantage of smaller band gaps, which result in increased adsorption capacity and photocatalytic effects. The results also showed the great effect of the examined GO–metal oxide nanocomposites on the decomposition of cationic rhodamine B dye, as indicated by steady-state absorption and fluorescence, time correlated single photon counting and nanosecond laser photolysis techniques. The antibacterial activity of the fabricated GO and GO–metal oxides has been studied against Gram-positive and Gram-negative bacteria.

The fabrication and characterization of graphene oxide–iron oxide and graphene oxide–iron oxide–zirconium oxide nanocomposites have been reported. The decomposition of cationic rhodamine B dye by both nanocomposites has been examined.     

Cd(ii) removal by Fe(ii) surface chemically modified layered double hydroxide–graphene oxide: performance and mechanism

Cd(ii) adsorption onto Fe(ii) modified Layered double hydroxide–graphene oxide (LDH–GO@Fe(ii)) was investigated using batch experiments. With the modification of Fe(ii), LDH–GO maintained its structure, while Fe(ii) species formed non-crystalline iron oxide clusters on the surface of the LDH/GO. A kinetics study indicated that adsorption obeyed a pseudo-second-order rate law. The equilibrium data were fitted well with the Langmuir isotherm model. The maximum adsorption capacity of LDH–GO@Fe(ii)₁₀ was 28.98 mg g⁻¹, higher those that of pure LDH–GO and LDH–GO@Fe(ii)₅₀. The increased sorption capacities could be explained by the increased specific surface area. Modification with Fe(ii) would lead to the generation of amorphous Fe oxides and Fe could occupy the binding sites for Cd(ii), thus excess Fe in the structure will restrain the adsorption of Cd(ii). The XRD and XPS patterns revealed the formation of Cd(OH)₂ after adsorption. Batch experiments indicated that precipitation and surface complexation were the main pathways for Cd(ii) removal.

Fe(ii)-decorated LDH–GO composites had a high capacity for Cd(ii) removal. The mechanisms were controlled by surface-induced precipitation and complex formation.     

CuI nanoparticle-catalyzed synthesis of tetracyclic benzo[e]benzo[4,5]imidazo[1,2-c][1,3]thiazin-6-imine heterocycles by SNAr-type C–S,C–N bond formation from isothiocyanatobenzenes and benzimidazoles

In this paper, a simple and practical synthesis of benzo[e]benzo[4,5]imidazo[1,2-c][1,3]thiazin-6-imine tetracyclic heterocycles via a CuI nanoparticle-catalyzed intramolecular C(sp²)–S coupling reaction is presented. This strategy provides a straightforward method for synthesizing analogs of the anti-HIV drug 3,4-dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine (PD 404182). The reaction rate and yield were increased by employing CuI nanoparticles.

We proposed a practical synthesis of analogs of the anti-HIV drug 3,4-dihydro-2H,6H-pyrimido[1,2-c][1,3]benzothiazin-6-imine via a CuI nanoparticle-catalyzed intramolecular C(sp²)–S coupling reaction.     

Decontamination of organic pollutants from aqueous media using cotton fiber–graphene oxide composite,utilizing batch and filter adsorption techniques: a comparative study

Cotton fiber–graphene oxide (C–GO) composite with high adsorptive properties towards the cationic dye, crystal violet (CV), was successfully fabricated by simple mixing of cotton fiber and GO in aqueous solution using a homogenizer. The as-prepared composite was characterized using TEM, SEM, LOM, XRD, FTIR, Raman and TGA. The characterization indicated that the formation of a homogeneous composite occurred via adequate mixing of the cotton fiber and GO. The fine structure of the obtained composite was successfully used in two adsorption techniques, namely batch adsorption and filter adsorption. Various parameters affecting batch adsorption, such as contact time, dye concentration, composite dose, NaCl dose, temperature and pH were investigated. In the filter adsorption mode, dye concentration, composite dose, NaCl dose, temperature, flow rate and pH were studied. A comparison study between the two techniques, i.e., batch adsorption and filter adsorption, are reported. The filter adsorption technique shows higher adsorption efficiency than the batch one, which was evident from the maximum adsorption capacity (Q°) values, obtained from the Langmuir isotherm. Further, the filter technique was developed and evaluated. This was achieved by regeneration, scaling-up and, finally, using another model of cationic dye (methylene blue).

Cotton fiber–graphene oxide (C–GO) composite with high adsorptive properties towards the cationic dye, crystal violet (CV), was successfully fabricated by simple mixing of cotton fiber and GO in aqueous solution using a homogenizer.     

Optimization and characterization of magnetite–reduced graphene oxide nanocomposites for demulsification of crude oil in water emulsion

Oily wastewater from the oil and gas industry negatively affects the environment. Oily wastewater typically exists in the form of an oil-in-water emulsion. Conventional methods to treat oily wastewater have low separation efficiency and long separation time and use large equipment. Therefore, a simple but effective method must be developed to separate oil-in-water emulsions with high separation efficiency and short separation times. Magnetite–reduced graphene oxide (M–RGO) nanocomposites were used as a demulsifier in this work. Magnetite nanoparticles (Fe₃O₄) were coated on reduced graphene oxide (rGO) nanosheets via an in situ chemical synthesis method. The synthesized M–RGO nanocomposites are environmentally friendly and can be recovered after demulsification by an external magnetic field. M–RGO characterization was performed using X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning microscopy, Raman spectroscopy, and vibrating sample magnetometry. Demulsification performance was evaluated in terms of M–RGO dosage, effects of pH, and brine concentration. The demulsification capability of M–RGO was determined based on the residual oil content of the emulsion, which was measured with a UV-vis spectrometer. The response surface method was used to determine the optimum conditions of the input variables. The optimum demulsification efficiency achieved at pH 4 and M–RGO dosage of 29 g L⁻¹ was approximately 96%. This finding demonstrates that M–RGO nanocomposites are potential magnetic demulsifiers for oily wastewater that contains oil-in-water emulsions. Also, the recyclability of this nanocomposite has been tested and the results shown that it is a good recyclable demulsifier.

Magnetite reduced graphene oxide were synthesized for separation of crude oil in water emulsion.     

Preparation of prolinamide with adamantane for aldol reaction catalysis in brine and separation using a poly(AN-MA-β-CD) nanofibrous film via host–guest interaction

Prolinamides with double-H potential were prepared and employed as organocatalysts in asymmetric aldol reactions. The catalyst with adamantane showed improved catalytic activity, which was further enhanced by using brine as the solvent. A series of aldol reactions in brine at 0 °C provided good yields (up to 98%) with high diastereoselectivities (>99 : 1) and enantioselectivities (>99%). The prepared catalyst was adsorbed by a nanofibrous film of poly(AN-MA-β-CD) via host–guest interaction in the reaction system. The catalyst was separated from the film by applying ultrasound, with a total recovery of 96.2%. The catalyst was reused up to five times without a significant change in diastereoselectivity and enantioselectivity.

Prolinamide with adamantane catalyzed the aldol reaction. The reaction of cyclohexanone with m-nitrobenzaldehyde assessed recyclability of catalyst. After run, the catalyst was adsorbed with nanofibrous of polymer via host–guest interaction.     

Highly efficient construction of an oxa-[3.2.1]octane-embedded 5–7–6 tricyclic carbon skeleton and ring-opening of the bridged ring via C–O bond cleavage

We report herein a highly efficient strategy for construction of a bridged oxa-[3.2.1]octane-embedded 5–7–6 tricyclic carbon skeleton through [3 + 2] IMCC (intramolecular [3 + 2] cross-cycloaddition), and the substituents and/or stereochemistries on C-4, C-6, C-7 and C-10 fully match those in the rhamnofolane, tigliane and daphnane diterpenoids. Furthermore, ring-opening of the bridged oxa-[3.2.1]octane via C–O bond cleavage was also successfully achieved.

We reported a highly efficient construction of an oxa-[3.2.1]octane-embedded 5–7–6 tricyclic carbon skeleton with a full match of the substituents and stereochemistries on C-4/-6/-7/-10 with those in the rhamnofolane/tigliane/daphnane diterpenoids.

Rhamnofolane, tigliane, and daphnane are three families of diterpenoids displaying a broad range of biological activities such as antiviral, anticancer, anti-HIV, immunomodulatory and neurotrophic activities.¹ Three representative members are neoglabrescin A² and curcusones I/J.³ The unique structural features of these three compounds include a 5–7–6 tricyclic carbon skeleton with a trans-fused 5–7 bicyclic skeleton, a 4,7-bridged oxa-[3.2.1]octane skeleton and a methylene (methyl) group at C-6 (Fig. 1). Some other related natural products include crotophorbolone,⁴ phorbol,⁵ prostratin,⁶ resiniferatoxin⁷ and curcusone A.⁸Open in a separate windowFig. 1Representative rhamnofolane/tigliane/daphnane diterpenes with a trans-fused 5–7 bicyclic skeleton, a 4,7-bridged oxa-[3.2.1]octane skeleton (corresponding structures with a ring-opening of the oxa-[3.2.1]octane via C–O cleavage) and a methylene (methyl) group at C-6.Due to their remarkable biological activities and unique and complex structures, these types of diterpenoids have drawn considerable attention from organic chemists, and many creative strategies have been developed for construction of the 5–7–6 tricycles with desirable substituents and stereochemistries on C-4, C-6, C-7 and C-10.⁹ Dai et al. reported the total syntheses of curcusones I and J by using an intramolecular Au-catalysed [4 + 3] cycloaddition for construction of the oxa-[3.2.1]octane-embedded 5–7-fused carbon skeleton and Diels–Alder [4 + 2] cycloaddition for construction of the additional 6-membered carbocycle (Scheme 1).^10a Some other natural products have been reported by the groups of Wender (phorbol, resiniferatoxin and prostratin),¹¹ Cha (phorbol),¹² Baran (phorbol),¹³ Xu/Li (prostratin),¹⁴ Liu (crotophorbolone),¹⁵ Inoue (crotophorbolone, resiniferatoxin, prostratin and related molecules)¹⁶ and Dai/Adibekian (curcusones A–D).^10b The groups of West^9c and Maimone^9h have reported attempts toward the total syntheses of related molecules through construction of a 4,7-bridged oxa-[3.2.1]octane skeleton respectively (Scheme 2).Open in a separate windowScheme 1Representative total syntheses of rhamnofolane/tigliane/daphnane diterpenes containing a 5–7–6 tricyclic carbon skeleton with a trans-fused 5–7 bicyclic skeleton and a 4,7-bridged oxa-[3.2.1]octane skeleton.Open in a separate windowScheme 2Representative synthetic strategies for construction of a bridged oxa-[3.2.1]octane-embedded 5–7–6 tricyclic carbon skeleton with desirable substituents and stereochemistries.We have previously reported a highly efficient construction of 5–7–6 tricyclic carbon skeleton with an intramolecular [4 + 3] IMPC (intramolecular [4 + 3] parallel-cycloaddition) of cyclopropane with dendralene/Diels–Alder [4 + 2] cycloaddition strategy.¹⁷ With this strategy, the fused 5–7 bicycle was efficiently constructed which matched the trans-stereochemisty, however a C-4 oxygen atom was not be direct. Following our previously developed [3 + 2] IMCC strategy,^18a–h we have recently reported a novel and efficient construction of a bridged aza-[3.2.1]octane-embedded 5–7–6 tricyclic carbon skeleton with desirable substituents and stereochemistries toward total syntheses of calyciphylline D-type Daphniphyllum alkaloids (Scheme 3).¹⁸ⁱ Herein, we report the application of the [3 + 2] IMCC strategy for efficient construction of the bridged oxa-[3.2.1]octane-embedded 5–7–6 tricycle with stereochemistries on C-4, C-7 and C-10, as well as a methylene (methyl) group at C-6 matching those in neoglabrescin A, curcusones I/J and related rhamnofolane/tigliane/daphnane diterpenes.Open in a separate windowScheme 3Proposed [3 + 2] IMCC strategy for construction of the bridged oxa-[3.2.1]octane-embedded 5–7–6 tricycle with suitable substituents and stereochemistries on C-4, C-6, C-7 and C-10.We started the research from benzyl bromide 2 which was prepared from a known compound 1 according to our recently reported method (Scheme 4).¹⁸ⁱ Compound 2 was then oxidized with NMO to afford aldehyde 3 which was used directly in the next step without further purification. Under catalysis of Sc(OTf)₃ (0.2 equiv.), the [3 + 2] IMCC of aldehyde 3 was successfully carried out to afford compound 4 in 82% yield over two steps. The structure of 4 was confirmed by X-ray crystal structure analysis.¹⁹ Hereto, the bridged oxa-[3.2.1]octane-embedded 5–7–6 tricycle have been successfully constructed, the substituents and stereochemistries on C-4, C-6, C-7 and C-10 fully match those in the corresponding natural products.Open in a separate windowScheme 4Construction of the bridged oxa-[3.2.1]octane-embedded 5–7–6 tricycle.With compound 4 in hand, we started to investigate the ring-opening of the bridged oxa-[3.2.1]octane via C–O bond cleavage (Scheme 5). Krapcho decarboxylation of 4 afforded monoester 5 in 88% yield as a mixture of two diastereoisomers in a ratio of nearly 1 : 1. Reduction of 5 with DIBAL-H at −78 °C afforded aldehyde 6 in 85% yield. To our delight, the oxa-bridge was opened under catalysis of TMSOTf²⁰ at −5 °C and a dehydration product 7 was obtained in 16% yield (brsm 53%) (21 conditions (Open in a separate windowScheme 5Ring-opening of the oxa-[3.2.1]octane via C–O bond cleavage.Ring-opening of the compound 6

The three-dimensional ordered macroporous structure of the Pt/TiO2–ZrO2 composite enhanced its photocatalytic performance for the photodegradation and photolysis of water

Using polystyrene (PS) spheres as a template, three-dimensional ordered macroporous Pt/TiO₂–ZrO₂ (3DOM Pt/TiO₂–ZrO₂) composites were prepared by vacuum impregnation combined with photoreduction. The crystal structure, composition, morphology, optical absorption, and surface physicochemical properties of the as-synthetized samples were characterized by X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (UV-vis/DRS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and N₂ adsorption–desorption analyses. The results showed that the 3DOM Pt/TiO₂–ZrO₂ composites were mainly composed of anatase TiO₂ and tetragonal ZrO₂ crystal phases, in which Pt mainly existed as a single species. In addition, the as-synthesized composites had open, three-dimensionally ordered macroporous structures that could enhance their multi-mode photocatalytic degradation performance under UV, visible light, simulated solar light, and microwave-assisted irradiation. Moreover, the 3DOM Pt/TiO₂–ZrO₂ composites exhibited the best photocatalytic water splitting performance as compared to other systems.

Using polystyrene spheres as templates, 3DOM Pt/TiO₂–ZrO₂ composites were prepared by the vacuum impregnation combined with photoreduction method, which exhibited an enhanced photodegradation and water splitting performance.