In situ synthesis of ZnO–GO/CGH composites for visible light photocatalytic degradation of methylene blue

A novel ZnO–GO/CGH composite was prepared using an in situ synthesis process for photodegradation of methylene blue under visible light illumination. The chitin–graphene composite hydrogel (CGH) was used to provide uniform binding of the nano ZnO–GO composite to the hydrogel surface and prevent their agglomeration. GO provides multi-dimensional protons and electron transport channels for ZnO with a flower-like structure, which possessed improved photo-catalytic activity. SEM analysis indicates that the hydrogel has good adsorption properties with rougher surfaces and porous microstructure, which enables it to adsorb the dyes effectively. Under synergetic enhancement of adsorption and photo-catalysis, catalytic activity and nano ZnO–GO/CGH recycling improved greatly. Synthesized nano ZnO–GO/CGH showed high dye removal efficiency of 99%, about 2.2 times that of the pure chitin gel under the same condition. This suggests the potential application of the new photocatalytic composites to remove organic dyes from wastewater.

A novel ZnO–GO/CGH composite was prepared using an in situ synthesis process for photodegradation of methylene blue under visible light illumination.     

In situ growth of novel carbon nanobuds and nanoballs on graphene nanosheets by the electrochemical method

Novel carbon nanostructures, carbon nanobuds and nanoballs in situ grown on graphene, have been synthesized by the electrochemical method in this study. Pristine graphene (GR) sheets were potentiostatic treated with sulfuric acid and were oxidized at 1.4–2.0 V constant potentials to obtain numerous nanobuds and peeled nanoballs. Scanning electron microscopy was used to determine the morphology of electrochemically treated GR nanosheets. Fourier transform infrared, X-ray diffraction analysis, and Raman spectroscopy were used to characterize the structure of samples. The above results indicate that amounts of nanobuds were in situ grown on the surface of GR sheets at a constant potential of 1.4 V was added to the GR electrode. With the constant potential increasing, the nanobuds grew into the nanoballs, exfoliating from the surface of graphene sheets, whereas the peroxidation of graphene sheets occurred at a higher potential of 2.0 V, leading to the formation of a large amount of graphene oxide fragments. Therefore, the optimal processing parameter of the formation of carbon nanoballs was under the constant potential of 1.8 V for 500 s.

Novel carbon nanostructures, carbon nanobuds and nanoballs in situ grown on graphene, have been synthesized by the electrochemical method in this study.     

In situ K2S activated electrospun carbon nanofibers with hierarchical meso/microporous structures for supercapacitors

Porous electrospun carbon nanofibers (CNFs) can be produced by a more advantageous ‘in situ activation’ method by electrospinning polyacrylonitrile (PAN) with an activation agent. However, most in situ activated electrospinning processes yield porous CNFs with rather limited surface area and less porosity due to the inappropriately selected activation agents. Here we found K₂S could perfectly meet both compatibility and reactivity requirements of PAN electrospinning to generate hierarchical meso/micropores inside electrospun CNFs. During the whole fabrication process, K₂S experiences a phase evolution loop and the hierarchical pore structures are formed by the reaction between K₂S oxidative derivatives and the as-formed carbon during heat treatment. The hierarchical meso/microporous CNFs not only showed a large surface area (835.0 m² g⁻¹) but also exhibited a high PAN carbonization yield (84.0 wt%) due to improved cyclization of PAN''s nitrile group during the pre-oxidation stage. As an electrode material for supercapacitors, the corresponding electrodes have a capacitance of 210.7 F g⁻¹ at the current density of 0.2 A g⁻¹ with excellent cycling durability. The hierarchically porous CNFs produced via in situ activation by K₂S combine the advantages of interconnected meso/micropores and are a promising candidate for electrochemical energy conversion and storage devices.

K₂S was found to be an excellent in situ activation agent for the fabrication of electrospun carbon nanofibers with large surface area (835.0 m² g⁻¹) and hierarchical meso/microporous structures.     

In situ green oxidation synthesis of Ti3+ and N self-doped SrTiOxNy nanoparticles with enhanced photocatalytic activity under visible light

A simple in situ green oxidation synthesis route was developed to prepare Ti³⁺ and N self-doped SrTiO_xN_y nanoparticles using TiN and H₂O₂ as precursors. X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) were used to characterize the crystallinity, structure and morphology. X-ray photoelectron spectroscopy (XPS) tests confirmed the presence of Ti³⁺ and N in the prepared SrTiO_xN_y nanoparticles. The resultant nanoparticles were shown to have strong absorption from 400 to 800 nm using UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The formation mechanism of the Ti³⁺ and N self-doped SrTiO_xN_y nanoparticles was also discussed. Under visible light irradiation, the obtained Ti³⁺ and N self-doped samples showed higher photocatalytic activity for the degradation of the model wastewater, methylene blue (MB) solution. The most active sample T-130-Vac, obtained at 130 °C under vacuum, showed a 9.5-fold enhancement in the visible light decomposition of MB in comparison to the commercial catalyst nano-SrTiO₃. The sample also showed a relatively high cycling stability for photocatalytic activity.

A simple in situ green oxidation synthesis route was developed to prepare Ti³⁺ and N self-doped SrTiO_xN_y nanoparticles using TiN and H₂O₂ as precursors.     

In situ synthesis of holey g-C3N4 nanosheets decorated by hydroxyapatite nanospheres as efficient visible light photocatalyst

The interesting g-C₃N₄ nanosheet morphology has drawn huge attention in photocatalytic applications because of its special features. Nonetheless, the relative activity of these nanosheets is still controversial due to the low available active sites and the high recombination probability of photo-induced charge carriers. In this work, in situ sol–gel approach was applied to synthesize holey g-C₃N₄ nanosheets/hydroxyapatite (HAp) nanospheres with plentiful in-plane holes. Herein, the presence of Ca²⁺ plays a key role in the formation of holey defects on 2D g-C₃N₄. In-plane holes provide nanosheets with more active edges and diffusion channelsv, resulting in a tremendous enhanced mass and photo-induced charge transfer speed. Moreover, the holes make highly numbered boundaries, which lead to the prevention of aggregation. On the other hand, distributed nano-HAp spheres on these nanosheets can form effective heterojunctions having high photo-degradation ability of pollutants. Intrinsic O-vacancies inside HAp unit cells mainly affect the capture of photogenerated electrons, pollutant molecules, and O₂ gas. The synergistic presence of O-vacancies and holey defects (C-vacancies) on 2D g-C₃N₄ plays a key role in raising the photocatalytic performance of holey g-C₃N₄/HAp. It can be concluded that the proposed preparation method is a promising approach for simultaneous synthesis of holey g-C₃N₄ and surface heterojunctions of Ca-based materials. This new structure has shown significant degradation ability of bisphenol A, a prominent pollutant, with a low amount (0.01 g) and short time.

The interesting g-C₃N₄ nanosheet morphology has drawn huge attention in photocatalytic applications because of its special features.     

In situ synthesis of TiO2/NC on cotton fibers with antibacterial properties and recyclable photocatalytic degradation of dyes

A cotton fabric/titanium dioxide-nanocellulose (TiO₂-Cot.) flexible and recyclable composite material with highly photocatalytic degradation of dyes and antibacterial properties was synthesized. During the preparation process, nano-TiO₂ particles were synthesized through an in situ strategy and grown on cotton fiber, and were wrapped with cellulose nanocrystals (NC). The prepared TiO₂-Cot. was characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The SEM and EDS results showed that nano-TiO₂ particles were evenly distributed on the fiber surface. The prepared TiO₂@Cot. has excellent photocatalytic efficiency of 95.68% for MB and 92.77% for AR under weak ultraviolet irradiation over 6 h. At the same time, it has excellent antibacterial activity against S. aureus and E. coli. The stability and reusability of the materials were also investigated.

A cotton fabric/titanium dioxide-nanocellulose (TiO₂-Cot.) flexible and recyclable composite material with highly photocatalytic degradation of dyes and antibacterial properties was synthesized.     

In situ fabrication of a direct Z-scheme photocatalyst by immobilizing CdS quantum dots in the channels of graphene-hybridized and supported mesoporous titanium nanocrystals for high photocatalytic performance under visible light

We report the considerable advantages of direct Z-scheme photocatalysts by immobilizing high-quality CdS quantum dots (QDs) in the channels of graphene-hybridized and supported mesoporous titania (GMT) nanocrystals (CdS@GMT/GR) under facile hydrothermal conditions. The photocatalysts have been characterized by XRD, PL, XPS, SEM, DRS, TEM, EIS, and N₂ adsorption. CdS QDs primarily serve as photosensitizers with a unique pore-embedded structure for the effective utilization of the light source. This direct Z-scheme CdS@GMT/GR exhibits higher photocatalytic activity than CdS/GR, GMT/GR, or CdS@MT. In addition, the rate constant of CdS@GMT/GR-2 is approximately twice the sum of those of CdS@MT and GMT/GR, because GR played the role of hole-transporting and collection layer as well as the hybridization level formation in terms of hybridizing MT and serving as a support. Therefore, the GR content tunes the energy band, affects the surface area, and controls the interfacial hole transfer and collection rate of the direct Z-scheme system. Furthermore, CdS@GMT/GR retains its high performance in repeated photocatalytic processes. This can be attributed to the fact that GR prevents QDs from photocorrosion by means of the hole-transporting and collection effect. A possible reaction mechanism is proposed. This work provides a promising strategy for the construction of highly efficient visible-light-driven photocatalysts to reduce the growing menace of environmental pollution.

CdS@GMT/GR exhibits high photocatalytic activity due to its direct Z-scheme structure obtained by immobilizing CdS quantum dots in the channels of GMT nanocrystals.     

In situ growth of PEDOT/graphene oxide nanostructures with enhanced electrochromic performance

Poly(3,4-ethylenedioxythiophene) (PEDOT)/graphene oxide (GO) hybrid nanostructures have been obtained by an in situ electro-polymerization process. Field emission scanning electron microscope observation indicates that the hybrid nanostructures consist of uniform and well-dispersed PEDOT nanoparticles integrated on the networked GO nanosheets. Surface chemistry and structure of the hybrid nanostructures have been characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Electrochemical and optical property measurements demonstrate that the hybrid nanostructures exhibit significantly improved electrochromic performance compared with the pristine PEDOT nanostructure. The contrast between coloring and bleaching state of the PEDOT nanostructure at 480 nm increases from 23.4% to 31.4% after hybridizing with GO nanosheets. The coloring time and bleaching time are shortened from 1800 ms to 300 ms and 1500 ms to 400 ms, respectively, while the coloring efficiency increases from 53.5 cm² C⁻¹ to 64.9 cm² C⁻¹ after the hybridization. The obtained PEDOT/GO hybrid nanostructures promise great potential in developing novel electrochromic materials for smart windows and other energy saving applications.

Designed growth of a novel PEDOT/graphene oxide (GO) hybrid and obtained hybrid demonstrates superior electrochromic performance.     

Z-scheme 2D-m-BiVO4 networks decorated by a g-CN nanosheet heterostructured photocatalyst with an excellent response to visible light

For economical water splitting and degradation of toxic organic dyes, the development of inexpensive, efficient, and stable photocatalysts capable of harvesting visible light is essential. In this study, we designed a model system by grafting graphitic carbon nitride (g-C₃N₄) (g-CN) nanosheets on the surface of 2D monoclinic bismuth vanadate (m-BiVO₄) nanoplates by a simple hydrothermal method. This as-synthesized photocatalyst has well-dispersed g-CN nanosheets on the surface of the nanoplates of m-BiVO₄, thus forming a heterojunction with a high specific surface area. The degradation rate for bromophenol blue (BPB) shown by BiVO₄/g-CN is 96% and that for methylene blue (MB) is 98% within 1 h and 25 min, respectively. The 2D BiVO₄/g-CN heterostructure system also shows outstanding durability and retains up to ∼95% degradation efficiency for the MB dye even after eight consecutive cycles; the degradation efficiency for BPB does not change too much after eight consecutive cycles as well. The enhanced photocatalytic activities of BiVO₄/g-CN are attributed to the larger surface area, larger number of surface active sites, fast charge transfer and improved separation of photogenerated charge carriers. We proposed a mechanism for the improved photocatalytic performance of the Z-scheme photocatalytic system. The present work gives a good example for the development of a novel Z-scheme heterojunction with good stability and high photocatalytic activity for toxic organic dye degradation and water splitting applications.

For economical water splitting and degradation of toxic organic dyes, the development of inexpensive, efficient, and stable photocatalysts capable of harvesting visible light is essential.     

In situ aluminium ions regulation for quantum efficiency and light stability promotion in white light emitting material

In this study, we have proposed an in situ ion regulation strategy to assemble a white-light-emitting material with high stability and efficiency. A fluorescence tunable hybrid material was first fabricated by a “ship around the bottle” method in which the fluorescent dyes, disodium 2-naphthol-3,6-disulfonate (R) and ZnO Quantum Dots (QDs), were embedded into metal–organic frameworks (MOFs) in proportion. Then, the competition coordination of aluminium ions over zinc ions to R were utilized to subtly adjust the intensity of blue fluorescence, leading to an ideal white light with Commission Internationale de l''Eclairage (CIE) coordinates of (0.30, 0.33) and a high Color-Rendering Index (CRI) value of 93%. Compared with the material fabricated by the ratio tuning of the R salt and ZnO QDs directly, the in situ ions regulation strategy enabled the final product to have a higher quantum efficiency and light stability. Moreover, this strategy also settled the non-tunable problem of fluorescence due to the competition coordination effects of aluminium ions and zinc ions in the same synthetic system. This synthetic strategy and our new findings can provide more ideas for designing new white-light-emitting materials.

An in situ ion regulation strategy to assemble white-light-emitting material with high stability and efficiency.     

In situ synthesis of monolayer graphene on silicon for near-infrared photodetectors

Direct integration of monolayer graphene on a silicon (Si) substrate is realized by a simple thermal annealing process, involving a top copper (Cu) layer as the catalyst and an inserted polymethylmethacrylate (PMMA) as the carbon source. After spin-coating the PMMA carbon source on the Si substrate, the Cu catalyst was deposited on PMMA/Si by electron beam evaporation. After that, graphene was directly synthesized on Si by decomposition and dehydrogenation of PMMA and the catalyzation effect of Cu under a simple thermal annealing process. Furthermore, under an optimized growth condition, monolayer graphene directly formed on the Si substrate was demonstrated. Utilizing the as-grown graphene/Si heterojunction, near-infrared photodetectors with high detectivity (∼1.1 × 10¹⁰ cm Hz^1/2 W⁻¹) and high responsivity (50 mA W⁻¹) at 1550 nm were directly fabricated without any post-transfer process. The proposed approach for directly growing graphene on silicon is highly scalable and compatible with present nano/micro-fabrication systems, thus promoting the application of graphene in microelectronic fields.

Direct integration of monolayer graphene on a silicon (Si) substrate is realized by a simple thermal annealing process, involving a top copper (Cu) layer as the catalyst and an inserted polymethylmethacrylate (PMMA) as the carbon source.     

In situ hybridization of an MXene/TiO2/NiFeCo-layered double hydroxide composite for electrochemical and photoelectrochemical oxygen evolution

Electrochemical and photoelectrochemical (PEC) oxygen evolution reactions (OER) are receiving considerable attention owing to their important roles in the overall water splitting reaction. In this contribution, ternary NiFeCo-layered double hydroxide (LDH) nanoplates were in situ hybridized with Ti₃C₂T_x (the MXene phase) via a simple solvothermal process during which Ti₃C₂T_x was partially oxidized to form anatase TiO₂ nanoparticles. The obtained Ti₃C₂T_x/TiO₂/NiFeCo-LDH composite (denoted as TTL) showed a superb OER performance as compared with pristine NiFeCo-LDH and comercial IrO₂ catalyst, achieving a current density of 10 mA cm⁻² at a potential of 1.55 V versus a reversible hydrogen electrode (vs. RHE) in 0.1 M KOH. Importantly, the composite was further deposited on a standard BiVO₄ film to construct a TTL/BiVO₄ photoanode which showed a significantly enhanced photocurrent density of 2.25 mA cm⁻² at 1.23 V vs. RHE under 100 mW cm⁻² illumination. The excellent PEC-OER performance can be attributed to the presence of TiO₂ nanoparticles which broadened the light adsorption to improve the generation of electron/hole pairs, while the ternary LDH nanoplates were efficient hole scavengers and the metallic Ti₃C₂T_x nanosheets were effective shuttles for transporting electrons/ions. Our in situ synthetic method provides a facile way to prepare multi-component catalysts for effective water oxidation and solar energy conversion.

An in situ prepared Ti₃C₂T_x/TiO₂/NiFeCo-LDH composite showed excellent performance in both electrochemical and photoelectrochemical oxygen evolution reactions.     

In situ template synthesis of hierarchical porous carbon used for high performance lithium–sulfur batteries

Hierarchical porous carbon (HPC) consists of micropores, mesopores and macrospores which are synthesized by in situ formation of template followed by acid etching. The obtained pores are three-dimensional and interconnected, and evenly distributed in the carbon matrix. By adjusting the ratio of the raw materials, the high specific surface area and large pore volume is afforded. The obtained HPC-3 samples possess graphite flakes and locally graphited-carbon walls, which provide good electrical conductivity. These unique characteristics make these materials suitable cathode scaffolds for Li–S batteries. After encapsulating 61% sulfur into HPC-3 host, the S/HPC-3 composite exhibits excellent cycling stability, high columbic efficiency, and superior rate cycling as a cathode material. The S/HPC-3 composite cathode displays an initial discharge capacity of 1059 mA h g⁻¹, and a reversible capacity of 797 mA h g⁻¹ after 200 cycles at 0.2C. The discharge capacities of the S/HPC-3 composite cathode after every 10 cycles at 0.1, 0.2, 0.5, 1, and 2C are 1119, 1056, 982, 921, and 829 mA h g⁻¹, respectively.

In situ template synthesis of HPCs used for lithium–sulfur batteries, which exhibits excellent cycling stability and superior rate cycling.     

In situ gelation of aqueous sulfuric acid solution for fuel cells

Aqueous sulfuric acid solution is a versatile liquid electrolyte for electrochemical applications and gelation of it has the advantages of easy shaping and reduced leaking. Herein, aqueous sulfuric acid solutions with concentrations of 1–4 mol L⁻¹ are fabricated into gel membranes by in situ polymerization of acrylamide as a monomer and divilynbenzene as a crosslinker for fuel cell applications. The gel membrane with an acid concentration of 3.5 mol L⁻¹ exhibited the maximum proton conductivity of 184 mS cm⁻¹ at 30 °C. Tensile fracture strength of the gel membrane reached 53 kPa with a tensile strain of 14. Thermogravimetric analysis reveals that the gel membranes are thermally stable at temperatures up to 231 °C. The gel membranes are successfully assembled into fuel cells and a peak power density of 74 mW cm⁻² is achieved. The fuel cell maintains steady operation over 200 h. In situ gelation of aqueous sulfuric acid solution offers an efficient strategy to prepare gel electrolytes for electrochemical devices.

In situ polymerization with acrylamide (AM) as the monomer and divinylbenzene (DVB) as a crosslinker in aqueous sulfuric acid solution resulted in gel membranes applicable in fuel cells.     

In situ formation of low molecular weight organogelators for slick solidification

We have investigated the in situ formation of Low Molecular Weight Organogelator (LMWO) molecules in oil-on-water slicks through dual reactive precursor injection. This method alleviates the need for any carrier solvent or prior heating, therefore reducing the environmental impact of LMWOs, giving instantaneous gelation, even at low temperatures (−5 °C). We show minimal leaching from our gels into the water layer.

Instantaneous gelation: a reactive precursors approach for the near-instant gelation of oil-on-water slicks down to −5 °C.

Low molecular weight organogelators (LMWOs or LMOGs) are small molecules designed to form supramolecular networks on addition to oil, turning the oil into a solid gel.^1–5 Once gelled, the oil can then be more easily removed. This makes LMWOs of great interest in the clean-up of marine oil and fuel spills, especially close to the shoreline or on bodies of inland water. A key advantage of LMWOs is that their properties can be designed to some extent at a molecular level⁴ insofar as one must ensure that the molecule will be able to form a supramolecular network with itself as well as ensuring solubility in the oil. Fig. 1(a) and (b) show the urea-based LMWOs used in this work, with hydrogen bonds between urea groups and π–π stacking between aromatic groups as examples of gelling intermolecular forces shown in Fig. 1(c). The lipophilic part of the LMWO grants the molecule solubility in oil as typically, the gelling intermolecular forces are polar in nature. Therefore, the synthesis of LMWOs often relies on balancing solubility in oil with polar intermolecular forces; too much hydrogen bonding, the compound will not be easily soluble, too little, and the compound simply will not gel.Open in a separate windowFig. 1(a) Reaction scheme of p-tolyl isocyanate “core” with a diisopropylamine “tail” forming N′-(4-methylphenyl)-N,N-dipropan-2-ylurea (referred to as compound 1), (b) reaction of p-tolyl isocyanate with dodecylamine forming N-dodecyl-N′-(4-methylphenyl)-urea (referred to as compound 2) (c) a scheme demonstrating the hypothetical self-assembly of urea-based LMWOs into supramolecular networks.Tolyl-isocyanates (“core” groups) are attractive precursors for urea based LMWOs, due to their ready availability from widespread use in poly(urethane) manufacture. They produce urea/urethane moieties on reaction with a nucleophile such as an amine or an alcohol, which readily hydrogen bond, giving the gelator the required intermolecular forces to form the supramolecular network in oils. These urea-based LMWOs have been widely characterised and explored.^1–4 The choice of nucleophilic “tail” (amine) is critical in order to impart solubility to the LMWO whilst still allowing the self-assembled structure to form. Previously, we have demonstrated a selection of p, m and o-tolyl isocyanates forming stable oil binding gels in sea water.⁹ In this study we examined the properties of a diisopropylamine/p-tolyl isocyanate system (Fig. 1(a)), and a dodecylamine/p-tolyl isocyanate system (Fig. 1(b)) with an eye to in situ application of the gel to an oil spill.It is the delivery of the LMWO to the hydrocarbon slick and gelation of the spill that remains a key challenge in environmental oil-spill remediation with LMWOs. The application of the LMWO to the oil has proven to be highly exacting simply due to the strength of the gelling intermolecular forces, and a successful LMWO will most commonly manifest itself as a solid. Therefore, in order to solubilise a solid LMWO in oil, energy (heat) has to be applied to the system to overcome these intermolecular forces and force dissolution. On mixing with the oil and cooling, the intermolecular forces can re-form and the oil will gel.This is a severe limitation of LMWOs in the oil-spill clean-up role, as they must either: (a) be applied hot, increasing deployment difficulty and energetic cost or (b) to hasten dissolution in oil, they would have to be deployed in a carrier solvent, increasing potential environmental consequences. Potentially, this is also a reason why LMWOs would only be suited to inshore clean-up as the cooling on aerial deployment would mean the LMWO would solidify before reaching the oil, preventing dissolution and gelation.Several groups have published investigations along these lines, such as: using heated solutions of LMWOs,^5,6 or supergelators dissolved in flammable ethanol/ethyl acetate blends of solvents to aid gel dissolution.^7–9 Sureshan et al. reported alkyl 4,6-O-benzylidene-glucopyranoside derivatives which can be applied as a powder and will gel oil mixtures on seawater⁵ and more recently, Zhang et al. reported d-gluconic acetal-based powder gelators able to gel oil slicks at room temperature.¹⁰Another emerging school of thought involved the combinatorial approach of LMWOs coupled with sorbents.¹¹ For example, the use of a supergelator (definition: a critical gelation concentration (CGC) of <0.1 wt%)¹² contained within a cellulose pulp matrix has been shown to be very effective at absorbing oil and affecting the release of the gelator into the oil.¹³ This approach alleviates the need for a carrier solvent and solves the problem of dissolution, but does require the presence of a solid matrix to work.In an alternative solution to the aforementioned challenges, we utilised the rapid reaction of isocyanate and amine to form a LMWO in situ, a method first utilised by Suzuki et al., who used the in situ synthesis of urea-based LMWOs to gel a variety of solvents in 2004. Here we extend the method to oil-on-sea water slicks.¹⁴ We also explore for the first time, the influence of temperature on in situ gelation, going below room temperature to more accurately simulate oceanic conditions. Herein we can report the successful, rapid gelation of 1-octadecene using compound 1 as a slick on cold seawater (−5 °C), an experiment essential for validating this method in cold environments.If two liquid precursors, such as diisopropylamine and p-tolyl isocyanate were sprayed into an oil in close proximity or one after another, a gel can form in the oil in situ, thus alleviating the need for elevated temperature or a carrier solvent. We examined this hypothesis by simulating an oil slick utilising 1-octadecene on deionised water, before rapid injection of equimolar amounts of p-tolyl isocyanate and amine (diisopropylamine (forming N′-(4-methylphenyl)-N,N-dipropan-2-ylurea), henceforth referred to as compound 1 or dodecylamine (forming N-dodecyl-N′-(4-methylphenyl)-urea), henceforth referred to as compound 2). On injection, either the isocyanate after the amine or vice versa (or indeed simultaneously), urea fibres began to form rapidly, completely gelling the 1-octadecene within 60 seconds (Fig. 2, ​,33 and ESI Video^†), even on slicks at low temperature on seawater at −5 °C (see Fig. S2^†). Rapid gelation within 60 seconds occurred with LMWO concentrations down to 2 wt% with the diisopropylamine/p-tolyl isocyanate system (1), and 5 wt% dodecylamine/p-tolyl isocyanate system (2), below which the reaction was slower with weaker gel consistency, and did not survive the “inversion test” (Fig. S1^†). We successfully managed to form an LMWO in situ in an oil on water slick, through rapid reaction of isocyanate and amine precursors, as shown by nuclear magnetic resonance (NMR) spectroscopy in the ESI.^† Indeed, water should compete for reaction with the isocyanate, but the localised high concentration precluded this. The NMR of the resulting gels did not show evidence of the isocyanate reaction with water in the oil slick, and no sequestered water in the oil. The resultant ureas and gelators were isolable from oil and could be extracted by distillation or centrifugation, as demonstrated in our previous work.⁴ We successfully repeated these experiments with kerosene and motor oil and several other oils at −5 °C (details in Table S1 ESI^†).Open in a separate windowFig. 2Scanning electron microscope images of xerogels of: (a) and (b) 10 wt% diisopropylamine/p-tolyl isocyanate system (compound 1), and (c) and (d) 10 wt% dodecylamine/p-tolyl isocyanate system (compound 2).Open in a separate windowFig. 3Photographs demonstrating the experimental protocol. (a) is gelator 1, the product from the reaction p-tolyl isocyanate with diisopropylamine, (b), (d) and (f) show the process of simultaneous injection of p-tolyl isocyanate and diisopropylamine into a 1-octadecene on water slick forming a gel in (f), (c) a 100 ml round bottom flask filled with water held back by a 1/1-octadecene gel and (e) illustrates complete separation of a 1/1-octadecene gel and water.The selected “cores” and “tails” are low molecular weight, with neither exceeding 320 g mol⁻¹. Precursors are all inexpensive (p-tolyl isocyanate is a poly(urethane) precursor) and alkyl amines which are readily available and inexpensive. The synthesis of ureas/carbamate from isocyanates and primary amines/alcohols is an instantaneous, facile one-pot reaction giving a pure product in high yield.⁴ Purification involved removal of the solvent (if any) and drying in vacuo. The process can easily be adapted to the kilogram scale, with prima facae evidence being the poly(urethane) industry. The LMWOs formed by this reaction are of unknown toxicity, but neither exhibited significant solubility in water, so are unlikely to pose a long-term threat to aquatic life.The in situ reaction was also very effective at gelling thin oil slicks (ca. 2 mm) and facilitated the collection of oil as evidenced in Fig. S3^† and ​and3e3e respectively. SEM images in Fig. 2 (xerogels of dodecylamine/p-tolyl isocyanate and diisopropylamine/p-tolyl isocyanate formed from gelling cyclohexane) demonstrate the formation of urea “tapes” in the same fashion as our previous work.⁴ The dodecylamine/p-tolyl isocyanate gel however formed more plate-like structures (Fig. 2(c) and (d)).The rapidity of reaction is very important for deployment of the in situ method system for fast clean-up of oil spills. Indeed, the use of diisopropylamine over dodecylamine facilitates a more rapid reaction, as evidenced by Video S2 in the ESI.^† We postulate that this is simply due to the small size of the diisopropylamine versus the dodecylamine, with the smaller diisopropylamine being able to react faster. Further to this, pump oil on river water (obtained from the River Thames near Kingston) was gelled successfully with both the dodecylamine/p-tolyl isocyanate and diisopropylamine/p-tolyl isocyanate systems. In terms of concentrations of precursors applied, we were able to invert 1 ml of 1-octadecene gels formed with the precursors applied against 2 ml of deionised water (see Fig. S4^†). The integrity of gels of 1 was maintained down to 1 wt%, whereas for 2, integrity was maintained down to 2 wt% of gelator.NMR spectroscopy confirmed that both gelators 1 and 2 were formed in high yield on reaction of p-tolyl isocyanate and diisopropylamine/dodecylamine respectively, in the absence of solvent (ESI^†). Furthermore, the same reagents reacted together successfully and in quantitative yields when added separately or together to a 1-octadecene layer on an aqueous layer. The gel formed in those cases dissolved fully in CDCl₃ with no significant amount of water present in the gel. This seemed to indicate no sequestration of water by the gel as it formed.One of the main problems with the approach outlined herein is toxicity. The safety datasheets (SDS) for both diisopropylamine and p-tolylisocyanate class them as irritants and as toxic. In order to ascertain the amount of precursors and gelator that leached into the aqueous phase, various slicks of 1-octadecene were created on seawater and river water before injection of precursors into the oil layer. The aqueous phases were then analysed for leachates by NMR. The results are summarised in

In situ synthesis of molybdenum carbide/N-doped carbon hybrids as an efficient hydrogen-evolution electrocatalyst

The development of non-precious metal based electrocatalysts for the hydrogen evolution reaction (HER) has received more and more attention over recent years owing to energy and environmental issues, and Mo based materials have been explored as a promising candidate. In this work, molybdenum carbide/N-doped carbon hybrids (Mo₂C@NC) were synthesized facilely via one-step high-temperature pyrolysis by adjusting the mass ratio of urea and ammonium molybdate. The Mo₂C@NC consisted of ultrasmall nanoparticles encapsulated by N-doped carbon, which had high specific surface area. They all exhibited efficient HER activity, and the Mo₂C@NC with a mass ratio of 160 (Mo₂C@NC-160) showed the best HER activity, with a low overpotential of 90 mV to reach 10 mA cm⁻² and a small Tafel slope of 50 mV dec⁻¹, which was one of the most active reported Mo₂C-based electrocatalysts. The excellent HER activity of Mo₂C@NC-160 was attributed to the following features: (1) the highly dispersed ultrasmall Mo₂C nanoparticles, which exhibited high electrochemically active surface areas; (2) the synergistic effect of the N-doped carbon shell/matrix, which facilitated the electron transport.

The molybdenum carbide/N-doped carbon hybrids (Mo₂C@NC) were synthesized facilely via one-step high-temperature pyrolysis, which exhibited efficient electrocatalytic hydrogen evolution performance.     

In situ growth of ZIF-67 on a nickel foam as a three-dimensional heterogeneous catalyst for peroxymonosulfate activation

Advanced oxidation processes based on sulfate radicals have been widely used to eliminate contaminants. In this study, an efficient cobalt-based three-dimensional heterogeneous catalyst was fabricated through in situ growth of ZIF-67 on nickel foam (NF/ZIF-67). The factors influencing NF/ZIF-67-activated peroxymonosulfate (PMS) were investigated. Enhanced RhB degradation was observed using NF/ZIF-67-activated PMS under neutral conditions and high temperatures. Sulfate radicals were the dominant active species for the oxidative decolorization of RhB with NF/ZIF-67-activated PMS. NF/ZIF-67 was easily separated from the solution, and it also retained high catalytic stability. This study provides a rapid and mild method for the fabrication of promising three-dimensional heterogeneous catalysts for PMS activation and wastewater treatment.

Macroscopic three-dimensional NF/ZIF-67 efficiently catalyzed peroxymonosulfate activation.     

In situ formation of Fe3O4/N-doped carbon coating on the surface of carbon fiber with improved electromagnetic wave-absorption property

Carbon fiber is an absorbing material with high strength, acid and alkali resistance, high temperature resistance, flexibility, and processability and plays an important role in the electromagnetic (EM) wave absorption of civil buildings and military equipment. However, its EM wave-absorption performance is poor because of its large complex permittivity and no magnetic loss ability. In this study, dopamine hydrochloride and FeCl₃ were used as precursors, and the Fe₃O₄/N-doped carbon coating was successfully grown in situ on the surface of short carbon fiber (SCF) via dopamine deposition, autopolymerization, FeCl₃ solution immersion, and calcination at high temperature to improve its EM wave-absorption property. The obtained Fe₃O₄/N-doped carbon particles were uniformly attached to the SCF in the form of a thin layer to constitute a unique hierarchical structure. The Fe₃O₄/N-doped carbon coating/SCF displayed an excellent EM wave-absorption performance. An effective bandwidth of 8.64 GHz and lowest reflection loss of −31.38 dB at 3 mm were achieved because of the significant reduction in complex permittivity and improvement in complex permeability, wave impedance, and EM loss ability of the SCF. The Fe₃O₄/N-doped carbon coating is expected to show great potential in EM wave-absorption fields.

Carbon fiber is an absorbing material with high strength, acid and alkali resistance, high temperature resistance, flexibility, and processability and plays an important role in the electromagnetic (EM) wave absorption of civil buildings and military equipment.     

N-doped TiO2 nanotube arrays with uniformly embedded CoxP nanoparticles for high-efficiency hydrogen evolution reaction

Efficient and stable non-precious metal based electrocatalysts are crucial to the hydrogen evolution reaction (HER) in renewable energy conversion. Herein, Co_xP nanoparticles (NPs) are uniformly embedded in N-doped TiO₂ nanotube arrays (Co_xP/N-TiO₂ NTAs) by low-temperature phosphorization of the precursor of metallic cobalt NPs embedded in N-doped TiO₂ NTAs (Co/N-TiO₂ NTAs) which were fabricated by phase separation of CoTiO₃ NTAs in ammonia. Owing to the abundant exposed surface active sites of Co_xP NPs, tight contact between the Co_xP NPs and TiO₂ NTAs, fast electron transfer in N-doped TiO₂, and channels for effective diffusion of ions and H₂ bubbles in the tubular structure, the Co_xP/N-TiO₂ NTAs have excellent electrocatalytic activity in HER exemplified by a low overpotential of 180 mV at 10 mA cm⁻² and small Tafel slope of 51 mV dec⁻¹ in 0.5 M H₂SO₄. The catalyst also shows long-term cycling stability and is a promising non-precious metal catalyst for HER.

Co_xP NPs embedded in N-doped TiO₂ NTAs was fabricated by phase separation of CoTiO₃ and delivers high efficient and stable HER performance in acid solution.     

In situ growth of Fe3O4 on montmorillonite surface and its removal of anionic pollutants

An environmentally functional material for the efficient removal of anionic pollutants in water was prepared for our study. Montmorillonite (M) was modified by hydrochloric acid (HCl) and cetyltrimethylammonium bromide (CTAB). Fe₃O₄ was grown in situ to prepare modified Fe₃O₄/montmorillonite (AC Fe₃O₄–Mt) composites. The number of hydroxyl sites on the surface of Mt and the surface tension were increased by HCl and CTAB modification, respectively, which enabled higher Fe₃O₄ surface growth, promoting the multi-directional crystallisation of Fe₃O₄ and improving reactivity. The XRD results show that Fe₃O₄ grows on the surface of Mt and has good crystallinity and high purity, meaning that AC Fe₃O₄–Mt is more reactive than Fe₃O₄. When AC Fe₃O₄–Mt is used to remove anionic pollutants in water, the removal effect under the synergistic action of adsorption-redox is significantly improved, and the maximum removable quantities of Cr(vi) and 2-4-dichlorophenol can reach 41.57 mg g⁻¹ and 239.33 mg g⁻¹, respectively. AC Fe₃O₄–Mt is a high efficiency and environmentally functional material with green environmental protection, which can be used in the field of sewage treatment.

An environmentally functional material for the efficient removal of anionic pollutants in water, was prepared for our study.