Goethite–titania composite: disinfection mechanism under UV and visible light

Goethite–titania (α-FeOOH–TiO₂) composites were prepared by co-precipitation and mechanical milling. The structural, morphological and optical properties of as-synthesized composites were characterized by X-ray powder diffraction, scanning electron microscopy and UV-Vis diffuse reflectance spectroscopy, respectively. α-FeOOH–TiO₂ composites and TiO₂-P25, as reference, were evaluated as photocatalysts for the disinfection of Escherichia coli under UV or visible light in a stirred tank reactor. α-FeOOH–TiO₂ exhibited better photocatalytic activity in the visible region than TiO₂-P25. The mechanical activation increased the absorption in the visible range of TiO₂-P25 and the photocatalytic activity of α-FeOOH–TiO₂. In the experiments with UV light and α-FeOOH–TiO₂, mechanically activated, a 5.4 log-reduction of bacteria was achieved after 240 min of treatment. Using visible light the α-FeOOH–TiO₂ and the TiO₂-P25 showed a 3.1 and a 0.7 log-reductions at 240 min, respectively. The disinfection mechanism was studied by ROS detection and scavenger experiments, demonstrating that the main ROS produced in the disinfection process were superoxide radical anion, singlet oxygen and hydroxyl radical.

A photocatalytic mechanism for FeOOH–TiO₂ composite is proposed under UV-Vis light, the FeOOH–TiO₂ composite showed higher photocatalytic activity than TiO₂-P25.     

Coating-free TiO2@β-SiC alveolar foams as a ready-to-use composite photocatalyst with tunable adsorption properties for water treatment

Coating-free TiO₂@β-SiC photocatalytic composite foams gathered within a ready-to-use shell/core alveolar medium the photocatalytically active TiO₂ phase and the β-SiC foam structure were prepared via a multi-step shape memory synthesis (SMS) replica method. They were fabricated following a sequential two-step carburization approach, in which an external TiC skin was synthesized at the surface of a β-SiC skeleton foam obtained from a pre-shaped polyurethane foam during a first carburization step. The adsorption behaviour of the shell/core TiO₂@β-SiC composite foams towards the Diuron pollutant in water was tuned by submitting the carbide foams to a final calcination treatment within the 550–700 °C temperature range. The controlled calcination step allowed (i) the selective oxidation of the TiC shell into a TiO₂ crystallite shell owing to the β-SiC resistance to oxidation and (ii) the amount of residual unreacted carbon in the foams to be tuned. The lower the calcination temperature, the more pronounced the adsorption profiles of the composites and the higher the Diuron amount removed by adsorption on the residual unreacted carbon. The ready-to-use TiO₂@β-SiC composite foams were active in the degradation of the Diuron pesticide, without any further post-synthesis immobilization or synthesis process at the foam surface. They displayed good reusability with test cycles and benefitted from an enhanced stability in terms of the titania release to water.

Coating-free TiO₂@β-SiC photocatalytic composite foams gathering within a ready-to-use shell/core alveolar medium the TiO₂ photocatalyst and the β-SiC foam structure were prepared via a multi-step shape memory synthesis (SMS) replica method.     

ZnCl2 loaded TiO2 nanomaterial: an efficient green catalyst to one-pot solvent-free synthesis of propargylamines

One-pot green synthesis of propargylamines using ZnCl₂ loaded TiO₂ nanomaterial under solvent-free conditions has been effectively accomplished. The aromatic aldehydes, amines, and phenylacetylene were reacted at 100 °C in the presence of the resultant catalyst to form propargylamines. The nanocrystalline TiO₂ was initially synthesized by a sol–gel method from titanium(iv) isopropoxide (TTIP) and further subjected to ZnCl₂ loading by a wet impregnation method. X-ray diffraction (XRD) patterns revealed the formation of crystalline anatase phase TiO₂. Field emission scanning electron microscopy (FESEM) showed the formation of agglomerated spheroid shaped particles having a size in the range of 25–45 nm. Transmission electron microscopy (TEM) validates cubical faceted and nanospheroid-like morphological features with clear faceted edges for the pure TiO₂ sample. Surface loading of ZnCl₂ on spheroid TiO₂ nanoparticles is evident in the case of the ZnCl₂ loaded TiO₂ sample. X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ti⁴⁺ and Zn²⁺ species in the ZnCl₂ loaded TiO₂ catalyst. Energy-dispersive X-ray (EDS) spectroscopy also confirmed the existence of Ti, O, Zn and Cl elements in the nanostructured catalyst. 15% ZnCl₂ loaded TiO₂ afforded the highest 97% yield for 3-(1-morpholino-3-phenylprop-2-ynyl)phenol, 2-(1-morpholino-3-phenylprop-2-ynyl)phenol and 4-(1,3-diphenylprop-2-ynyl)morpholine under solvent-free and aerobic conditions. The proposed nanostructure-based heterogeneous catalytic reaction protocol is sustainable, environment-friendly and offers economic viability in terms of recyclability of the catalyst.

A one-pot green synthesis of propargylamines using nanostructured ZnCl₂–TiO₂ under solvent-free conditions has been effectively accomplished. The proposed reaction protocol is sustainable, environment-friendly and offers economic viability.     

The synthesis of HMF-based α-amino phosphonates via one-pot Kabachnik–Fields reaction

The first use of biomass-derived HMF in the one-pot Kabachnik–Fields reaction is reported here. A wide range of furan-based α-amino phosphonates were prepared in moderate to excellent yields under mild, effective and environmentally-benign conditions: iodine as a non-metal catalyst, biobased 2-MeTHF as the solvent and room or moderate temperature. The hydroxymethyl group of HMF persists in the Kabachnik–Fields products, widening the scope of further modification and derivatization compared to those arising from furfural. Issues involving the diastereoselectivity and double Kabachnik–Fields condensation were also faced.

A mild and efficient one-pot protocol for the synthesis of α-amino phosphonates directly from 5-HMF was described.

Recently, the production of chemicals from renewable biomass has attracted growing interests due to the dwindling reserves of fossil resources and the increasing awareness of environmental concerns.¹ 5-Hydroxymethylfurfural (HMF), a promising primary biomass-derived platform chemical readily obtained from acid-catalyzed dehydration of six-carbon carbohydrates, displays a strong potential in organic synthesis.² Besides the well-developed conversions of HMF towards monomers and biofuels via oxidation or reduction reactions,³ some remarkable strategies converting HMF to high value-added fine chemicals have been disclosed.⁴ Nevertheless, the specific reactivity and reduced stability of HMF, in comparison with the pentose-derived furfural homolog, have limited its use in synthetic applications.⁵ Furthermore, its commercial availability, though not anymore a barrier nowadays, has limited the number of investigations in the past. In this regard, developing efficient and economic routes to existing or novel fine chemicals from HMF, with its different reactivity compared to simpler aldehydes, is still a challenge.Multi-component reactions (MCRs) are extremely convenient and efficient strategies to prepare highly functionalized compounds from simple starting materials by one-pot procedures. Since they have many advantages, such as high atom economy, high convergence, time and energy saving, MCRs have gained much attention in modern synthetic organic chemistry.⁶ Nevertheless, to our knowledge, the direct utilization of HMF in MCR processes has been only rarely explored.α-Amino phosphonates, due to the structural analogy to natural α-amino acids and their significant biological activities, such as antitumor, antitubercular, cytotoxic activities, and so on,⁷ have been the subject of considerable interest in the past decades both in synthetic organic and medicinal chemistry.⁸ Among several methods for preparing α-amino phosphonates, the Kabachnik–Fields reaction, a one-pot condensation of an aldehyde, an amine and a dialkyl phosphite is the most effective and convenient strategy.⁹ A large number of conditions have been reported for the acid-catalyzed (Lewis/Brønsted)¹⁰ and catalyst-free¹¹ Kabachnik–Fields reaction, affording the α-amino phosphonates from various aldehydes. However, none of studies have included HMF as a substrate in their scope although the products from HMF can offer more possibilities for further functionalization, thanks to its CH₂OH appendage. The sole synthesis of α-amino phosphonates from HMF was reported by Cottier and Skowroński in a two-step reaction strategy, consisting in pre-formation of the imine which upon isolation reacted with dialkyl phosphites as nucleophilic species at high temperature using trifluoroacetic acid as catalyst.¹² Thus, a milder and more direct procedure for the synthesis of α-amino phosphonates from HMF is still to be developed.As part of our on-going interest on the application of HMF towards fine chemicals and on green and sustainable chemistry,¹³ we explored the possibility to synthesize furan-based α-amino phosphonates via the one-pot Kabachnik–Fields condensation, directly from HMF.For this study, we selected molecular iodine as a mild and effective Lewis acid catalyst, as often used in multicomponent synthesis because of its operational simplicity, low cost and toxicity and likely to be compatible with HMF sensitivity to acidic conditions.¹⁴ Wu and co-workers have confirmed its efficiency in Kabachnik–Fields reactions of simple aldehydes such as benzaldehyde and furfural.¹⁵ The primary set of experimental conditions has been fixed as 5 mol% iodine in ethanol [0.5 M] with equimolar stoichiometric ratio of all partners (HMF, aniline, diethyl phosphite). The corresponding Kabachnik–Fields product 4a was obtained in 71% isolated yield after 24 h, together with around 11% of unreacted HMF and 6% of the intermediate imine (

Synthesis of core–shell N-TiO2@CuOx with enhanced visible light photocatalytic performance

In this paper, a core–shell N-TiO₂@CuO_x nanomaterial with increased visible light photocatalytic activity was successfully synthesized using a simple method. By synthesizing ammonium titanyl oxalate as a precursor, N-doped TiO₂ can be prepared, then the core–shell structure of N-TiO₂@CuO_x with a catalyst loading of Cu on its surface was prepared using a precipitation method. It was characterized in detail using XRD, TEM, BET, XPS and H₂-TPR, while its photocatalytic activity was evaluated using the probe reaction of the degradation of methyl orange. We found that the core–shell N-TiO₂@CuO_x nanomaterial can lessen the TiO₂ energy band-gap width due to the N-doping, as well as remarkably improving the photo-degradation activity due to a certain loading of Cu on the surfaces of N-TiO₂ supports. Therefore, a preparation method for a novel N, Cu co-doped TiO₂ photocatalyst with a core–shell structure and efficient photocatalytic performance has been provided.

In this paper, a core–shell N-TiO₂@CuO_x nanomaterial with increased visible light photocatalytic activity was successfully synthesized using a simple method.     

Cationic palladium(ii)-catalyzed synthesis of substituted pyridines from α,β-unsaturated oxime ethers

An efficient method for the synthesis of multi-substituted pyridines from β-aryl-substituted α,β-unsaturated oxime ethers and alkenes via Pd-catalyzed C–H activation has been developed. The method, using Pd(OAc)₂ and a sterically hindered pyridine ligand, provides access to various multi-substituted pyridines with complete regioselectivity. Mechanistic studies suggest that the pyridine products are formed by Pd-catalyzed electrophilic C–H alkenylation of α,β-unsaturated oxime followed by aza-6π-electrocyclization. The utility of this method is showcased by the synthesis of 4-aryl-substituted pyridine derivatives, which are difficult to synthesize efficiently using previously reported Rh-catalyzed strategies with alkenes.

An efficient method for the synthesis of multi-substituted pyridines from α,β-unsaturated oxime ethers via cationic Pd(ii)-catalyzed C–H activation has been developed.     

An efficient access to β-ketosulfones via β-sulfonylvinylamines: metal–organic framework catalysis for the direct C–S coupling of sodium sulfinates with oxime acetates

A copper-based framework Cu₂(OBA)₂(BPY) was synthesized and used as a recyclable heterogeneous catalyst for the synthesis of β-sulfonylvinylamines from sodium sulfinates and oxime acetates via direct C–S coupling reaction. The transformation was remarkably affected by the solvent, and chlorobenzene emerged as the best option. This Cu-MOF displayed higher activity than numerous conventional homogeneous and MOF-based catalysts. The catalyst was reutilized many times in the synthesis of β-sulfonylvinylamines without considerably deteriorating in catalytic efficiency. These β-sulfonylvinylamines were readily converted to the corresponding β-ketosulfones via a hydrolysis step with aqueous HCl solution. To the best of our knowledge, this direct C–S coupling reaction to achieve β-sulfonylvinylamines was not previously conducted with a heterogeneous catalyst.

Cu₂(OBA)₂(BPY) was used as catalyst for the synthesis of β-sulfonylvinylamines from sodium sulfinates and oxime acetates. These β-sulfonylvinylamines were readily converted to corresponding β-ketosulfones via a hydrolysis step.     

Enhanced charge separation in TiO2/nanocarbon hybrid photocatalysts through coupling with short carbon nanotubes

The interfacial contact between TiO₂ and graphitic carbon in a hybrid composite plays a critical role in electron transfer behavior, and in turn, its photocatalytic efficiency. Herein, we report a new approach for improving the interfacial contact and delaying charge carrier recombination in the hybrid by wrapping short single-wall carbon nanotubes (SWCNTs) on TiO₂ particles (100 nm) via a hydration-condensation technique. Short SWCNTs with an average length of 125 ± 90 nm were obtained from an ultrasonication-assisted cutting process of pristine SWCNTs (1–3 μm in length). In comparison to conventional TiO₂–SWCNT composites synthesized from long SWCNTs (1.2 ± 0.7 μm), TiO₂ wrapped with short SWCNTs showed longer lifetimes of photogenerated electrons and holes, as well as a superior photocatalytic activity in the gas-phase degradation of acetaldehyde. In addition, upon comparison with a TiO₂–nanographene “quasi-core–shell” structure, TiO₂-short SWCNT structures offer better electron-capturing efficiency and slightly higher photocatalytic performance, revealing the impact of the dimensions of graphitic structures on the interfacial transfer of electrons and light penetration to TiO₂. The engineering of the TiO₂–SWCNT structure is expected to benefit photocatalytic degradation of other volatile organic compounds, and provide alternative pathways to further improve the efficiency of other carbon-based photocatalysts.

The interfacial contact between TiO₂ and graphitic carbon in a hybrid composite plays a critical role in electron transfer behavior, and in turn, its photocatalytic efficiency.     

A novel superparamagnetic powerful guanidine-functionalized γ-Fe2O3 based sulfonic acid recyclable and efficient heterogeneous catalyst for microwave-assisted rapid synthesis of quinazolin-4(3H)-one derivatives in Green media

The novel organic–inorganic nanohybrid superparamagnetic (γ-Fe₂O₃@CPTMS–guanidine@SO₃H) nanocatalyst modified with sulfonic acid represents an efficient and green catalyst for the one-pot synthesis of quinazolin-4(3H)-one derivatives via three-component condensation reaction between anthranilic acid, acetic anhydride and different amines under microwave irradiation and solvent-free conditions (4a–q). XRD, FT-IR, FE-SEM, TGA, VSM and EDX were used to characterize this new magnetic organocatalyst. Outstanding performance, short response time (15–30 min), simple operation, easy work-up procedure, and avoidance of toxic catalysts can be regarded as its significant advantages. Moreover, it can be easily separated from the reaction solution through magnetic decantation using an external magnet, and recycled at least six times without notable reduction in its activity.

A novel organic–inorganic nanohybrid superparamagnetic nanocatalyst (γ-Fe₂O₃@CPTMS–guanidine@SO₃H) represents an efficient and green catalyst for the one-pot synthesis of quinazolin-4(3H)-one derivatives via a three-component condensation reaction.     

Microwave synthesised Pd–TiO2 for photocatalytic ammonia production

Palladium doped anatase TiO₂ nanoparticles were synthesised by a rapid (3 min) one-pot microwave synthesis technique at low temperature and pressure. After being fully characterised by SEM, XRD, Raman, XPS and EDX, photocatalytic nitrate reduction and ammonia production were studied over various dopant levels between 0–3.97 wt% Pd and compared to similar previous literature. Improved yields of ammonia were observed with most dopant levels when compared to non-doped microwave synthesised TiO₂ with 2.65 wt% found to be the optimum dopant level producing 21.2 μmol NH₃. Electrochemical impedance spectroscopy of TiO₂ and Pd–TiO₂ photoelectrodes revealed improvements in charge transfer characteristics at high Pd dopant levels.

A rapid 3 minute one-pot microwave synthesis of Pd–TiO₂ showing improved activity for photocatalytic nitrate reduction into ammonia.     

Enhanced photocatalytic water splitting of a SILAR deposited α-Fe2O3 film on TiO2 nanoparticles

We have investigated the effect of deposition of a α-Fe₂O₃ thin layer on a substrate of TiO₂ nanoparticles for photoelectrochemical (PEC) water splitting. The TiO₂ layer was coated on an FTO substrate using the paste of TiO₂ nanoparticles. The α-Fe₂O₃ layer was deposited on the TiO₂ thin film, using the method of Successive Ionic Layer Adsorption and Reaction (SILAR) with different cycles. Various characterizations including XRD, EDX and FE-SEM confirm the formation of α-Fe₂O₃ and TiO₂ nanoparticles on the electrode. The UV-visible absorption spectrum confirms a remarkable enhancement of the absorption of the α-Fe₂O₃/TiO₂/FTO composite relative to the bare TiO₂/FTO. In addition, the photocurrents of the composite samples are remarkably higher than the bare TiO₂/FTO. This is mainly due to the low band gap of α-Fe₂O₃, which extends the absorption spectrum of the α-Fe₂O₃/TiO₂ composite toward the visible region. In addition, the impedance spectroscopy analysis shows that the recombination rate of the charge carriers in the α-Fe₂O₃/TiO₂ is lower than that for the bare TiO₂. The best PEC performance of the α-Fe₂O₃/TiO₂ sample was achieved by the sample of 70 cycles of α-Fe₂O₃ deposition with about 7.5 times higher photocurrent relative to the bare TiO₂.

Optimization of photoelectrochemical water splitting by a composite of SILAR-deposited α-Fe₂O₃ thin film on a substrate of TiO₂ nanoparticles.     

Copper-catalyzed synthesis of α-ketoamides using water and dioxygen as the oxygen source

The reaction employing H₂O and O₂ as the co-oxygen source in the catalytic synthesis of α-ketoamides is described. This copper-catalyzed reaction is carried out in a tandem manner constituted by the hydroamination of alkyne, hydration of vinyl–Cu complex and subsequent oxidation. Isotope labeling and radical capture experiments reveal that the oxygen atom of α-ketone at α-ketoamides derives from O₂ and the oxygen atom of amide group originates from H₂O.

The reaction employing H₂O and O₂ as the co-oxygen source in the catalytic synthesis of α-ketoamides is described. This Cu-catalyzed reaction is carried out in a tandem manner constituted by hydroamination of alkyne, hydration of vinyl–Cu complex and subsequent oxidation.     

Visible light-induced oxidative α-hydroxylation of β-dicarbonyl compounds catalyzed by ethylenediamine–copper(ii)

We have developed an efficient oxidative α-hydroxylation of β-keto esters with firstly using the structurally simple ethylenediamine–copper(ii) as a catalyst for β-keto esters activation and using visible light as the driving force for generating more active singlet oxygen (¹O₂) from triplet state oxygen (³O₂) in the air, providing a series of α-hydroxy β-keto esters in excellent yields (up to 99%) under extremely low photosensitizer loading (0.01 mol%) and catalyst loading (1 mol%) within a short time. Moreover, the gram-scale synthesis showed the practical utility of this protocol.

An efficient visible light-induced oxidative α-hydroxylation of β-dicarbonyl compounds has been developed using structurally simple ethylenediamine–copper(ii) as a catalyst.     

Fullerene–porphyrin hybrid nanoparticles that generate activated oxygen by photoirradiation

The preparation of water-dispersible hybrid nanoparticles comprising fullerene and porphyrin from cyclodextrin complexes is described. In the presence of polyethylene glycol, C₆₀ fullerene and porphyrin were expelled from the cyclodextrin cavity to form fullerene–porphyrin hybrid nanoparticles in water. The fullerene–porphyrin hybrid nanoparticles exhibit improved singlet oxygen generation ability under photoirradiation compared with that of C₆₀ nanoparticles.

Hybrid nanoparticles comprising fullerene and porphyrin are formed via guest exchange reaction of cyclodextrin complexes. The hybrid nanoparticles exhibit singlet oxygen generation ability under photoirradiation.

Water-dispersible colloidal fullerene assemblies, referred to as fullerene nanoparticles (NPs), have recently received increasing attention.^1–3 Fullerene NPs are negatively charged and can be dispersed in water in the absence of any solubilizer. Fullerene NPs demonstrate promise within biological and medical applications, as radical scavengers and photosensitizers for photodynamic therapy. To further extend the applications of fullerene NPs, additional hybridization with desired functional molecules is required. Porphyrin and associated derivatives are highly promising candidates for hybridization with fullerenes to increase photoactivity.⁴ Numerous studies on the complexation of fullerenes with porphyrin molecules using synthetic organic chemistry^5–7 or supramolecular chemistry^8–10 have been reported. Although fullerene NPs have been intensively studied over the last decade, no reliable method to achieve the hybridization of porphyrins with fullerene NPs has been proposed.Poly(ethylene glycol) monomethyl ether (PEG) was recently observed to accelerate the decomposition of fullerene C₆₀–γ-CD complexes in water, which leads to the rapid aggregation of C₆₀ to form water-dispersible C₆₀ NPs.¹¹ In this method, C₆₀–γ-CD complexes can exist as stable isolated molecules in water, enabling the precise size control and step-wise growth of C₆₀ NPs.^12,13 Herein, the preparation of hybrid NPs comprising C₆₀ and hydrophobic porphyrin molecules are reported. C₆₀–γ-CD and porphyrin-trimethyl-β-cyclodextrin (por–TMe-β-CD) complexes are mixed in water in the presence of PEG. Both complexes decompose through the interaction of PEG with the CDs, leading to the formation of C₆₀–porphyrin hybrid NPs (denoted as C₆₀–por NPs). The C₆₀–por NPs are negatively charged and easily disperse in water. Additionally, the ability of C₆₀–por NPs to generate activated oxygen is also evaluated.The C₆₀–γ-CD complex^14,15 and 1–TMe-β-CD complex (Fig. 1)^16–18 were prepared according to a previously described procedure (see the ESI^† for details). The ¹H NMR spectrum of the mixed solution comprising the C₆₀–γ-CD complex and PEG after 1 h incubation at 80 °C shows that the peaks attributed to the C₆₀–γ-CD complexes completely disappeared (Fig. S1^†). Hence, the ¹H NMR data confirm the decomposition of the C₆₀–γ-CD complexes and the formation of water-dispersible C₆₀ NPs, as previously reported.^11–13 The effect of PEG on 1–TMe-β-CD complexes was also investigated by ¹H-NMR as shown in Fig. S2.^† After incubating the mixed solution of 1–TMe-β-CD complex and PEG ([1] = 0.1 mM, [PEG] = 5.0 g L⁻¹) for 1 h at room temperature, peaks attributed to the 1–TMe-β-CD complex were still evident at 4.97 ppm and above 7.7 ppm (Fig. S2(i)^†). Hence, PEG has no influence upon the 1–TMe-β-CD structure at room temperature. Conversely, after incubating for 1 h at 80 °C, a dark purple precipitate formed and the aforementioned ¹H NMR peaks completely disappeared (Fig. S2(ii)^†). In the absence of PEG, the 1–TMe-β-CD complex was stable in water both at room temperature (Fig. S2(iii)^†) and 80 °C (Fig. S2(iv)^†). These results suggest a decomposition route of 1–TMe-β-CD by interaction with PEG at 80 °C, with a concomitant formation of non-dispersible large aggregates.Open in a separate windowFig. 1Chemical structures of porphyrin derivatives used in this study.To obtain hybrid NPs comprising C₆₀ and 1 (C₆₀–1 NPs), PEG (M_w = 2000) was added to an aqueous solution containing C₆₀–γ-CD and 1–TMe-β-CD complexes ([C₆₀] = [1] = 0.1 mM, [PEG] = 5.0 g L⁻¹), which were thereafter incubated at room temperature or 80 °C. The ¹H NMR spectrum of the mixed solution at room temperature shows peaks attributed to γ-CD in the C₆₀–γ-CD complex at 5.03 ppm, TMe-β-CD in the 1–TMe-β-CD complex at 4.97 ppm, and 1 in the 1–TMe-β-CD complex in the region of 7.6–8.5 ppm (Fig. 2a(i)). The data indicate that PEG fails to induce the decomposition of the C₆₀–γ-CD and 1–TMe-β-CD complexes at room temperature. Conversely, after the mixture was heated at 80 °C for 1 h, the peaks attributed to the C₆₀–γ-CD and 1–TMe-β-CD complexes completely disappeared (Fig. 2a(ii)). Hence, C₆₀–γ-CD and 1–TMe-β-CD were decomposed at 80 °C, in the presence of PEG. The solution after being subjected to heat treatment at 80 °C for 1 h, was dark purple in the absence of any precipitate. The hydrodynamic diameter and ζ-potential of the reacted solution were 125 nm (polydispersity index = 0.21) and −20.2 mV, respectively. Water dispersible fullerene NPs typically exhibit negative ζ-potentials, the origin of which still requires elucidating.^19,20 Hence, the formation of water-dispersible nano-composites, C₆₀–1 NPs, is suggested.Open in a separate windowFig. 2(a) ¹H NMR spectra of mixed solutions comprising fullerene C₆₀–γ-cyclodextrin (CD) and 1–trimethyl (TMe)-β-CD complexes ([C₆₀] = [1] = 0.1 mM) (i) before and (ii) after heating at 80 °C for 1 h, in the presence of polyethylene glycol (PEG) (5 g L⁻¹). Open circles: free γ-CD, filled circles: C₆₀–γ-CD, open diamonds: free TMe-β-CD, and filled diamonds: porphyrin–TMe-β-CD (por–TMe-β-CD) complex. The spectra at 7.6–8.5 ppm, are amplified five-fold. (b) Ultraviolet-visible (UV/Vis) absorption spectra of the mixed solution comprising C₆₀–γ-CD and 1–TMe-β-CD complexes ([C₆₀] = [1] = 0.1 mM) with PEG (5 g L⁻¹), before (dashed line) and after (solid line) heating at 80 °C for 1 h. (c) UV/Vis absorption spectra of the mixed solution comprising the C₆₀–γ-CD complex as a function of the 1–TMe-β-CD complex concentration ([C₆₀] = 0.1 mM, [1] = 0–0.2 mM) with PEG (5 g L⁻¹) after heating at 80 °C for 1 h.The por–TMe-β-CD complexes using 2–6 (Fig. 1), were also prepared adopting the same procedure as that for the 1–TMe-β-CD complex. Each por–TMe-β-CD complex solution was mixed with C₆₀–γ-CD and PEG ([C₆₀] = [por] = 0.1 mM, [PEG] = 5.0 g L⁻¹). The ¹H NMR spectrum of each individual mixed solution after being incubated for 1 h at 80 °C, is shown in Fig. S3.^† In the ¹H NMR spectrum of the mixture comprising C₆₀–γ-CD and 2–TMe-β-CD, the peaks attributed to these complexes at 5.03, 4.98, and 7.60–8.50 ppm, completely disappeared after being subjected to incubation for 1 h at 80 °C, without precipitation (Fig. S3a^†). Similar changes in the ¹H NMR spectrum of the mixture comprising C₆₀–γ-CD and 3–TMe-β-CD complexes are observed, as shown in Fig. S3b.^† The data suggest that the 2–TMe-β-CD and 3–TMe-β-CD complexes can be decomposed in a similar manner as the C₆₀–γ-CD complexes, and imply the formation of C₆₀–2 and C₆₀–3 NPs.The ¹H NMR spectra of the mixed solutions comprising C₆₀–γ-CD and 4, 5, or 6–TMe-β-CD complexes failed to show peaks attributed to the C₆₀–γ-CD complex, and peaks associated with the respective por–TMe-β-CD complexes were observed after incubation for 1 h at 80 °C (Fig. S3c–e,^† respectively). Hence, the data suggest that the C₆₀–γ-CD complex decomposed in the presence of PEG, and the 4, 5, and 6–TMe-β-CD complexes were observed to be stable without decomposition at 80 °C. There have been reports suggesting the strong interaction of water-soluble tetraphenyl porphyrins with TMe-β-CDs.^21,22 Polar substituents prompt the penetration of the polarized porphyrin rims into the TMe-β-CD cavity. Porphyrins 4–6 possess polar substituents, which are suggested to enable the formation of stable TMe-β-CD complexes. Furthermore, the size of the β-CD cavity is sufficiently narrow to prevent any strong interaction with PEG.²³ Thus, PEG-induced decomposition of the 4, 5, and 6–TMe-β-CD complexes is not possible.The absorption behavior of C₆₀–1 NPs was investigated using ultraviolet-visible (UV/Vis) spectroscopy. In the UV/Vis spectra, the characteristic peak of solvated C₆₀–γ-CD, at 333 nm shifted to 344 nm after heating at 80 °C for 1 h (Fig. 2b). An additional broad absorption at 400–550 nm is also apparent, which is characteristic of solid-state crystalline C₆₀ and arises from the electronic interactions between adjacent C₆₀ molecules.^24,25 The characteristic peak of the solvated 1–TMe-β-CD complex at 415 nm, shifted to 432 nm, with induced broadening after being subjected to heat treatment at 80 °C for 1 h (Fig. 2b). In the absence of C₆₀–γ-CD complexes, the characteristic absorption peak attributed to the solvated 1–TMe-β-CD complex completely disappeared after heating for 1 h at 80 °C, in the presence of PEG (Fig. S4^†). The data show that 1, when expelled from the TMe-β-CD cavities, forms non-dispersible precipitates in the absence of C₆₀. For 1 dispelled from the TMe-β-CD cavities to be stably dispersed in water, formation of co-aggregates with C₆₀ may be a prerequisite. C₆₀–2 and C₆₀–3 NPs also show similar UV-Vis absorption spectra after being subjected to heating at 80 °C for 1 h, as shown in Fig. S5a and b,^† respectively.To further elucidate the composite formation of C₆₀ and 1, the influence of 1 concentration on C₆₀–1 NP formation was investigated by UV/Vis spectroscopy (Fig. 2c). The intensity of the absorption peak at 432 nm increased as a function of 1 concentration from 0.05 to 0.1 mM. Conversely, the absorption peak at 345 nm, derived from the formation of fullerene NPs, shifted to 338 nm, with increasing concentration of 1. This absorption peak derives from the fullerene nanoparticle size, and as the size decreased (i.e., the NPs became smaller), the peak blue-shifted.¹¹ The results suggest that in the presence of 1, the fullerene interaction might be disturbed, or smaller C₆₀ NPs might form. For C₆₀–1 NPs formulated with 0.2 mM of 1 ([C₆₀] = 0.1 mM, [1] = 0.2 mM), the absorption peak derived from the Soret band of 1 split into two peaks (Fig. 2c). The absorption peak at the shorter wavelength of 415 nm is consistent with that of the 1–TMe-β-CD complex. The absorption peak at the longer wavelength of 431 nm is almost consistent with the absorption peaks in the UV/Vis spectra of C₆₀–1 NPs fabricated with 0.05 and 0.1 mM of 1. The findings indicate that in the sample comprising 0.2 mM of 1, a portion of the 1–TMe-β-CD complexes remained in the complex state after heating for 1 h at 80 °C, in the presence of PEG. The absorption peak at 338 nm, which reflects the state of fullerene NPs, is similar to that of C₆₀–1 NPs fabricated with 0.1 mM of 1. When C₆₀ and 1 form co-aggregated NPs, the ratio of 1 to C₆₀ is thought to be limited to ∼1 : 1.Morphological observations of the hybrid NPs were also undertaken. In the absence of the por–TMe-β-CD complex, C₆₀ NPs possessing fairly monodisperse size distributions were observed (Fig. S6a^†). The average diameter of the individual NPs, determined from the transmission electron microscopy (TEM) images, is 82 nm. C₆₀ NPs have been previously reported to exhibit lattice fringes and diffraction patterns, which suggests that C₆₀ NPs maintain the face-centered cubic (fcc) crystalline structure.¹¹ C₆₀–1 NPs prepared with 0.05 mM C₆₀ and 0.1 mM 1, possessed irregular shapes (Fig. 3a and b, respectively). The average diameter of C₆₀–1 NPs, determined by TEM, is 119 nm (Fig. 3a and S6b^†), demonstrating the larger C₆₀–1 NP size than that of the C₆₀ NPs (82 nm). Increasing the concentration of 1 to 0.1 mM results in the average diameter of C₆₀–1 NPs to increase to 131 nm (Fig. 3b and S6c^†). Similar morphology is observed from the TEM micrographs of C₆₀–2 and C₆₀–3 NPs having average diameters of 109 nm and 144 nm, respectively (Fig. 3c and d, respectively). A lower PEG molecular weight or a lower reaction temperature during C₆₀ NP formation via C₆₀–γ-CD complexes have been reported to induce an increase in the diameter of the C₆₀ NPs.^11,12 Thus, the findings suggest that slower reaction conditions result in less nucleation and a larger NP formation. Porphyrin 3 possesses a methoxy substituent at the para position of the phenyl group and is more polar than 1 or 2. Previous reports have demonstrated that the higher the polarity of the phenyl group, the more stable the complex with TMe-β-CD,^21,22 which indicates that 3–TMe-β-CD is more stable than 1– or 2–TMe-β-CD in water. Thus, the aforementioned decomposition, which results from the interaction with PEG, is slower in 3 with a concomitant increase in the NP size.Open in a separate windowFig. 3Transmission electron microscopy (TEM) images of C₆₀–1 nanoparticles (NPs) prepared with (a) 0.05 and (b) 0.1 mM of the 1–TMe-β-CD complex. TEM images of (c) C₆₀–2 and (d) C₆₀–3 NPs. Scale bars in images (a–d) are 100 nm. (e) High resolution TEM micrograph and selected-area electron diffraction pattern of C₆₀–1 NP. Scale bar is 10 nm. (f) ¹³C NMR spectra of (i) C₆₀ NPs and (ii) C₆₀–1 NPs. (g) Illustration of a C₆₀–por NP. A portion of C₆₀ form crystalline structures, while a portion of the porphyrin molecules interact with C₆₀ at the molecular level.In the high-resolution TEM micrograph (Fig. 3e), the C₆₀–1 NPs only exhibited partial lattice fringes, and hence did not show clear diffraction patterns compared with the C₆₀ NPs (inset in Fig. 3e).¹¹ The findings demonstrate the highly amorphous nature of the C₆₀–1 NPs, and that the C₆₀ crystal structure was only retained in part. ¹³C NMR spectra also provide important information about the structure of the C₆₀–1 NPs. A characteristic C₆₀ cluster signal at 142.4 ppm was detected in both C₆₀ NPs and C₆₀–1 NPs (Fig. 3f).²⁶ The C₆₀–1 NP dispersions also exhibited several small new signals at 141.5, 143.3, and 143.7 ppm, as shown in Fig. 3f(ii). When a fullerene and a porphyrin molecule form a stable complex in solution, the C₆₀ signal shifts depending on the interaction type between the fullerene and the porphyrin molecule.²⁷ Thus, the porphyrin molecule interacted with the aggregate of C₆₀ in C₆₀–1, as illustrated in Fig. 3g.Some porphyrin molecules can form a co-crystal with fullerene C₆₀.²⁸ To form a crystal structure, not only the interaction between molecules but also the relationship with the solvent, such as gradually changing the polarity of the solvent or removing the solvent, are important. In our system, porphyrin molecules that are pseudo-dissolved by TMe-β-CDs are added to water, which is a poor solvent for porphyrins, through the interaction of PEG with TMe-β-CDs. The porphyrin molecule should immediately aggregate and have difficulty forming a crystal structure. Furthermore, because water is also a poor solvent for fullerene C₆₀, C₆₀ also immediately aggregates in water. Thus, it should be extremely difficult for C₆₀ and porphyrin molecules to regularly associate to form a co-crystal structure.The concentration of singlet oxygen molecules (¹O₂, Type-II energy transfer pathway) generated by photoirradiation was measured according to a chemical method using 9,10-anthracenediyl-bis(methylene) dimalonic acid (ABDA)^15,29 as a marker to determine the biological activities of C₆₀ NPs, C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs. The absorption of ABDA at the absorption maximum (380 nm) was monitored as a function of irradiation time ([C₆₀] = 0.1 mM, [por] = 0 or 0.1 mM). Under visible-light irradiation at wavelengths > 620 nm, C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs generated higher levels of ¹O₂ than C₆₀ (Fig. 4a). These results show that the ¹O₂ photoproduction abilities of the C₆₀–por NPs were higher than that of the C₆₀ NPs. There are no significant differences in the ¹O₂ photoproduction abilities of C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs, which suggests that the structure of the porphyrin has an insignificant influence on the ability of the hybrid NPs. The generation of formazan, via the reduction of nitroblue tetrazolium (NBT) by oxygen radicals (O₂˙⁻), is observed as an increase of absorption intensity at 560 nm.³⁰ The reduction of NBT by O₂˙⁻ was scarcely detected in solutions containing C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs under photoirradiation, even though formazan was readily detected in the positive control sample in the presence of reduced nicotinamide adenine dinucleotide (NADH) (Fig. 4b). The results suggest that the reactive oxygen species produced by C₆₀–1 NPs, C₆₀–2 NPs, and C₆₀–3 NPs are predominantly ¹O₂ generated by a Type-II reaction.¹⁸Open in a separate windowFig. 4(a) ¹O₂ generation by NPs. Bleaching of 9,10-anthracenediyl-bis(methylene) dimalonic acid (ABDA) was monitored as a function of the decrease in the absorbance at 380 nm, for C₆₀ NPs (black circles and solid line), C₆₀–1 NPs (red circles and solid line), C₆₀–2 NPs (blue circles and solid line), and C₆₀–3 NPs (green circles and solid line) ([C₆₀] = 15 μM, [por] = 0 or 15 μM, [ABDA] = 25 μM). (b) O₂˙⁻ generation by NPs. The amount of formazan generated by the reduction of nitroblue tetrazolium (NBT) in the presence of O₂˙⁻ was analyzed by the absorbance at 560 nm, of C₆₀–1 NPs (red circles) and C₆₀–2 NPs (blue circles) in the absence (solid lines) and presence (dashed lines) of NADH ([C₆₀] = 15 μM, [por] = 15 μM, [NBT] = 200 μM, [NADH] = 0 or 625 μM). All samples were photoirradiated at >620 nm, in O₂-saturated aqueous solutions.In summary, the preparation of hybrid C₆₀–porphyrin NPs was achieved via a guest exchange reaction comprising porphyrin CD complexes and C₆₀. Seven C₆₀–por NP derivatives with various moieties were prepared. CD porphyrin complexes possessing phenyl and methoxyphenyl moieties were decomposed in the presence of PEG at the same time as C₆₀–γ-CD complexes and formed NPs with C₆₀. Porphyrins containing a hydrophilic moiety form stable complexes with TMe-β-CD and fail to co-aggregate with C₆₀. The C₆₀–por NPs are negatively charged and are easily dispersed and stable in water. The ¹O₂ generation ability of C₆₀–por NPs under photoirradiation (>620 nm) is greater than that of C₆₀ NPs. The findings herein demonstrate a new method to fabricate fullerene–porphyrin composite materials, which provides a route to highly functional fullerene-based materials.     

Global minimum beryllium hydride sheet with novel negative Poisson's ratio: first-principles calculations

As one of the most prominent metal-hydrides, beryllium hydride has received much attention over the past several decades, since 1978, and is considered as an important hydrogen storage material. By reducing the dimensionality from 3 to 2, the beryllium hydride monolayer is isoelectronic with graphene; thus the existence of its two-dimensional (2D) form is theoretically feasible and experimentally expected. However, little is known about its 2D form. In this work, by a global minimum search with the particle swarm optimization method via density functional theory computations, we predicted two new stable structures for the beryllium hydride sheets, named α–BeH₂ and β–BeH₂ monolayers. Both structures have more favorable thermodynamic stability than the recently reported planar square form (Nanoscale, 2017, 9, 8740), due to the forming of multicenter delocalized Be–H bonds. Utilizing the recently developed SSAdNDP method, we revealed that three-center-two-electron (3c–2e) delocalized Be–H bonds are formed in the α–BeH₂ monolayer, while for the β–BeH₂ monolayer, novel four-center-two-electron (4c–2e) delocalized bonds are observed in the 2D system for the first time. These unique multicenter chemical bonds endow both α– and β–BeH₂ with high structural stabilities, which are further confirmed by the absence of imaginary modes in their phonon spectra, the favorable formation energies comparable to bulk and cluster beryllium hydride, and the high mechanical strength. These results indicate the potential for experimental synthesis. Furthermore, both α– and β–BeH₂ are wide-bandgap semiconductors, in which the α–BeH₂ has unusual mechanical properties with a negative Poisson''s ratio of −0.19. If synthesized, it would attract interest both in experiment and theory, and be a new member of the 2D family isoelectronic with graphene.

As one of the most prominent metal-hydrides, beryllium hydride has received much attention over the past several decades, since 1978, and is considered as an important hydrogen storage material.     

TiO2–Au composite nanofibers for photocatalytic hydrogen evolution

TiO₂-based materials for photocatalytic hydrogen (H₂) evolution have attracted much interest as a renewable approach for clean energy applications. TiO₂–Au composite nanofibers (NFs) with an average fiber diameter of ∼160 nm have been fabricated by electrospinning combined with calcination treatment. In situ reduced gold nanoparticles (NPs) with uniform size (∼10 nm) are found to disperse homogenously in the TiO₂ NF matrix. The TiO₂–Au composite NFs catalyst can significantly enhance the photocatalytic H₂ generation with an extremely high rate of 12 440 μmol g⁻¹ h⁻¹, corresponding to an adequate apparent quantum yield of 5.11% at 400 nm, which is 25 times and 10 times those of P25 (584 μmol g⁻¹ h⁻¹) and pure TiO₂ NFs (1254 μmol g⁻¹ h⁻¹), respectively. Furthermore, detailed studies indicate that the H₂ evolution efficiency of the TiO₂–Au composite NF catalyst is highly dependent on the gold content. This work provides a strategy to develop highly efficient catalysts for H₂ evolution.

The H₂ production rate of TiO₂–Au nanofibers is dramatically improved to 12 440 μmol g⁻¹ h⁻¹, 10 times that of pure TiO₂.     

An expeditious synthesis of 6,7-dihydrodibenzo[b,j][4,7] phenanthroline derivatives as fluorescent materials

A rapid and efficient method has been developed for the synthesis of 13,14-dimethyl-6,7-dihydrodibenzo[b,j][4,7]phenanthroline derivatives (3a–d) through the Friedländer condensation of 2-aminoarylketone with 1,4-cyclohexanedione under solvent-free conditions using p-toluenesulphonic acid. The synthetic utility of compounds 3a, 3b, and 3c was demonstrated by synthesizing compounds 6a–kvia Suzuki coupling, 8 by Buchwald–Hartwig amination, and 9a–bvia NBS bromination. Significantly, the emission band corresponding to the π–π* electronic transition of compounds 3a, 6a, 6d, 6f, and 8 showed a redshift with increasing polarity of the solvents. Molar extinction coefficient (ε), Stoke''s shift (Δ ), and quantum yield (Φ_f) were calculated for all these compounds.

A rapid method has been developed for the synthesis of 13,14-dimethyl-6,7-dihydrodibenzo[b,j][4,7]phenanthroline derivatives (3a–d) through the Friedländer condensation of 2-aminoarylketone with 1,4-cyclohexanedione under neat conditions using p-TSA.     

Deposition of platinum on boron-doped TiO2/Ti nanotube arrays as an efficient and stable photocatalyst for hydrogen generation from water splitting

An efficient photocatalyst of boron-doped titanium dioxide/titanium nanotube array-supported platinum particles (Pt–B/TiO₂/Ti NTs) was fabricated for photocatalytic water splitting for hydrogen production through a two-step route. First, B/TiO₂/Ti NTs were prepared by anodic oxidation using hydrofluoric acid as electrolyte and boric acid as a B source. Then, Pt particles were deposited on the surface of B/TiO₂/Ti NTs by photo-assisted impregnation reduction. The structure and properties of Pt–B/TiO₂/Ti NTs were characterized by various physical measurements which showed the successful fabrication of Pt–B/TiO₂/Ti NTs. The Pt–B/TiO₂/Ti NTs, with a B-doping content of 15 mmol L⁻¹, showed the highest photocatalytic activity and exhibited a photocatalytic hydrogen-production rate of 384.9 μmol g⁻¹ h⁻¹, which was 9.2-fold higher than that of unmodified TiO₂/Ti NTs (41.7 μmol g⁻¹ h⁻¹). This excellent photocatalytic performance was ascribed mainly to the synergistic effect of Pt and B, which could enhance the photocatalytic activity of TiO₂/Ti NTs.

Pt–B/TiO₂/Ti NTs, prepared by anodic oxidation and photo-deposition methods, showed excellent photocatalytic activity.     

Synthesis of hierarchical nanocrystalline β zeolite as efficient catalyst for alkylation of benzene with benzyl alcohol

To develop an efficient solid acid catalysts for the Friedel–Crafts alkylation reaction, especially for involving bulky molecules, the direct synthesis of hierarchical nanocrystalline β zeolites were achieved by using amphiphilic organosilane ([(CH₃O)₃SiC₃H₆N(CH₃)₂C₁₈H₃₇]Cl, TPOAC) as collaborative structure-directing agent (SDA). The growth evolution of β crystals and the influence of TPOAC/SiO₂ molar ratio on the mesoporous structure, crystal size, and acidic properties of β zeolites were investigated and discussed in detail. The characterization results reveal that intracrystalline mesopores and intercrystalline mesopores/macropores via the stacking of β nanocrystals were generated over the hierarchical β zeolites. Moreover, most of the strong acid sites were well remained compared with the conventional microporous β zeolite. Consequently, the hierarchical nanocrystalline β zeolite synthesized under the optimized synthesis conditions shows improved specific catalytic activity of acid sites (turnover number, TON) in alkylation of benzene with benzyl alcohol, which can be attributed to the integrated balance of considerable mesoporosity, accessibility of the acid sites, and well-remained strong acid sites in the hierarchical β zeolite.

Hierarchical β zeolite with enhanced transport and specific catalytic activity of acid sites in Friedel–Crafts alkylation was achieved by using amphiphilic organosilane surfactant as mesopores-directing agent and crystal growth inhibitor.     

Mn-based catalysts supported on γ-Al2O3, TiO2 and MCM-41: a comparison for low-temperature NO oxidation with low ratio of O3/NO

Mn-Based catalysts supported on γ-Al₂O₃, TiO₂ and MCM-41 synthesized by an impregnation method were compared to evaluate their NO catalytic oxidation performance with low ratio O₃/NO at low temperature (80–200 °C). Activity tests showed that the participation of O₃ remarkably promoted the NO oxidation. The catalytic oxidation performance of the three catalysts decreased in the following order: Mn/γ-Al₂O₃ > Mn/TiO₂ > Mn/MCM-41, indicating that Mn/γ-Al₂O₃ exhibited the best catalytic activity. In addition, there was a clear synergistic effect between Mn/γ-Al₂O₃ and O₃, followed by Mn/TiO₂ and O₃. The characterization results of XRD, EDS mapping, BET, H₂-TPR, XPS and TG showed that Mn/γ-Al₂O₃ had good manganese dispersion, excellent redox properties, appropriate amounts of coexisting Mn³⁺ and Mn⁴⁺ and abundant chemically adsorbed oxygen, which ensured its good performance. In situ DRIFTS demonstrated the NO adsorption performance on the catalyst surface. As revealed by in situ DRIFTS experiments, the chemically adsorbed oxygen, mainly from the decomposition of O₃, greatly promoted the NO adsorption and the formation of nitrates. The Mn-based catalysts showed stronger adsorption strength than the corresponding pure supports. Due to the abundant adsorption sites provided by pure γ-Al₂O₃, under the interaction of Mn and γ-Al₂O₃, the Mn/γ-Al₂O₃ catalyst exhibited the strongest NO adsorption performance among the three catalysts and produced lots of monodentate nitrates (–O–NO₂) and bidentate nitrates (–O₂NO), which were the vital intermediate species for NO₂ formation. Moreover, the NO–TPD studies also demonstrated that Mn/γ-Al₂O₃ showed the best NO desorption performance among the three catalysts. The good NO adsorption and desorption characteristics of Mn/γ-Al₂O₃ improved its high catalytic activity. In addition, the activity test results also suggested that Mn/γ-Al₂O₃ exhibited good SO₂ tolerance.

The Mn/γ-Al₂O₃ catalyst exhibited excellent performance for NO conversion in the presence of a low ratio of O₃/NO, which was due to the coexistence of Mn³⁺ and Mn⁴⁺ and abundant chemically adsorbed oxygen.