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A carbon-coated Magnéli phase Ti4O7 composite has been successfully synthesised, via modified carbonthermal reduction of amorphous TiO2, which was prepared from hydrolysis of titanium sulphate and polyvinyl alcohol, at a relatively low temperature and fast reaction rate. Moreover, the effect of heat treatment temperature and time on the reduced phases is revealed. Despite removal of oxide ions, scanning electron microscopic images clearly show the obtained carbon-coated Ti4O7 composite retains well the spherical morphology of the precursor, and the high-pressure pelleted treatment effectively inhibits the growth of the final product during the heat treatment process. In addition, the prepared composite with mesopore structure exhibits a Brunauer, Emmett, and Teller (BET) surface area as high as 84.495 m2 g−1 and good electrochemical stability in alkaline electrolyte, as well as some oxygen reduction reaction catalytic activity. The results presented in this work open an avenue for its potential electrochemical applications.
A novel material of Ag3PO4–Ag–Bi2WO6 Z-scheme heterojunction has been successfully synthesised using a simple deposition–precipitation method. In this work, the authors used diverse techniques to characterise the structure, catalytic performance, and morphology of the prepared materials. Meanwhile, the catalytic performance of prepared materials was evaluated by degrading organic pigment. The excellent catalytic performance of the material is according to the collaboration of Ag nanoparticles in the Ag3PO4–Ag–Bi2WO6 heterojunction. Ag nanoparticles enhance the stableness and activeness of the catalyst by acting as a charge transfer bridge between Ag3PO4 and Bi2WO6, which results in improving electron–hole pairs’ separation. Compared with pure Bi2WO6 and Ag3PO4–Bi2WO6 materials, Ag3PO4–Ag–Bi2WO6 has higher decomposition effectiveness of methylene blue under the same conditions. The photocatalytic mechanism was put forward and the process of the hole–electron pair's separation is discussed in detail, which is due to the formation of the Z-scheme heterojunction with Ag nanoparticles acted as a charge transfer bridge.
Biogenetic nanocomposites research provides valuable methods for the green synthesis of nanomaterials. As a dissimilatory metal-reducing bacterium, Shewanella oneidensis MR-1 is used to reduce Ag+ to Ag nanoparticles (Ag NPs) (diameter about 10 nm) under anaerobic conditions, resulting in the in-situ formation of Ag NPs immobilised on TiO2 nanotubes (TNTs) (Ag/TNTs nanocomposites). The loading amount of Ag nanocrystals on the TNT surface can be controlled easily through adjusting the AgNO3 concentration and further influence visible-light absorption efficiency of Ag/TNTs nanocomposites by decreasing the Ag loading amount. Ag/TNTs nanocomposites show superior photocatalytic efficiency under simulated sunlight than single TiO2 nanomaterials. Moreover, the photocatalytic capacity of Ag/TNTs nanocomposites synergistic by S. oneidensis MR-1 is further enhanced and the degradation ratio of methylene blue reaches 92.3% within 30 min which attributed to a synergistic effect.
Glassy carbon electrode (GCE) modified with aluminium hydroxide/iron hydroxide/multi-walled carbon nanotubes (AH/IH/MWCNTs) composites has been prepared by a simple method and applied for dihydro-nicotinamide adenine dinucleotide (NADH) detection. AH/IH can not only accelerate electron transfer but also electrostatically interact with the phosphate groups of NADH through iron hydroxide to improve the sensitivity of the sensor. Meanwhile, MWCNTs served as a bonding agent to provide a built-in conductor, which resulted in boosted electron transfer at the interface. Compared with the GCE, MWCNTs–GCE, and AH/MWCNTs–GCE, the AH/IH/MWCNTs–GCE exhibited an extraordinary electrocatalytic response towards NADH, with a wide linear concentration range from 0.5 to 220 μM with a low-detection limit of 0.30 μM, at a comparatively low potential (+0.15 V versus Ag/AgCl). Moreover, alcohol dehydrogenase was used as a model system for the design of a sensitive ethanol biosensor. The resulting biosensor exhibited an ethanol sensitivity of 9 μA/mM, a concentration range of 20–400 μM, and a detection limit of 5 μM. These results demonstrate the potential of the AH/IH/MWCNTs nanocomposite film for biosensors in combination with NADH-producing enzymes.
Tin dioxide (SnO2) photocatalyst has broad prospects for the degradation of toxic organic pollutants; however, its practical application is greatly hampered by poor activity due to the high recombination rates of photogenerated electron-hole pairs. In this work, titania (TiO2) modified SnO2 photocatalysts were obtained by a facile hydrothermal method to suppress the rapid recombination of photogenerated electron-hole pairs and improve the photocatalytic activity. Ultraviolet–visible (UV–vis)_ diffuse reflectance spectra suggest that TiO2–SnO2 composite photocatalysts hold stronger UV light absorption ability than that of the pure SnO2. Surface photovoltage spectroscopy and photoelectrochemistry results show that the separation rate of photogenerated charge pairs of TiO2–SnO2 photocatalysts was greatly enhanced. The photocatalytic activities of the photocatalysts were evaluated by the decay of rhodamine B (RhB) under UV irradiation illumination. The results display that modification of SnO2 by TiO2 can largely enhance the photocatalytic activity and the photocatalytic performance of 0.5:1-TS sample is nearly 5 times that of the pure SnO2. Moreover, maintaining the ratio of TiO2 and SnO2 at 0.5:1, the amount of catalyst was 30 mg, the concentration of dye was 10 mg/l, and the pH of RhB solution was 2, the sample has the best photocatalytic activity.
Biocatalysis has the potential to enable green chemistry. New methods of enzyme immobilisation will be required to improve enzyme stability, product purification, and compatibility of different enzymes in the same reaction conditions. Deoxyribonucleic acid (DNA) stands out among supramolecular scaffolds, as simple Watson–Crick base-pairing rules can be used to rationally design a unique nanoscale environment around each individual enzyme in a cascade. Enhancements of enzyme activity and stability on DNA nanostructures have previously been reported, but never in the context of industrially relevant chemical syntheses or reaction conditions. Here, the authors show DNA can enhance the activity and stability of a galactose oxidase mutant, which could be used in a cascade to produce bioplastics from lignin. The enzyme was enhanced in the cell-free extract, which to their knowledge has not been shown before for any enzymes on DNA. This is significant because crude biocatalytic reactions are vastly more cost-effective. This opens the door to further work on multienzyme cascades by tuning the properties of individual enzymes.
Hierarchical porous zinc oxide (ZnO)/silver (Ag) microspheres were prepared by two-step method. The porous ZnO microspheres were prepared firstly, and then Ag nanoparticles were evenly anchored on the surface of ZnO microspheres by Sn2+ activation method. The results show that ZnO is wurtzite phase, and Ag particles are only coated on the surface of ZnO microspheres. Compared with pure ZnO, there are two obvious absorption peaks of Ag-doped ZnO, which corresponds to the ultraviolet absorption peak of ZnO and the plasma resonance absorption peak of Ag, respectively. The intensities of photoluminescence peak of ZnO/Ag microspheres are significantly lower than that of pure ZnO. Moreover, ZnO/Ag microspheres show higher photocatalytic activity than ZnO, which may be attributed to the existence of highly dispersed Ag.
The flower-like and hexagonal flake-like ZnO microstructures were synthesised by a microwave method using ammonia water and sodium hydroxide as precipitant, respectively. The products were characterised by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction and photoluminescence. The photocatalytic activity of the flower-like and hexagonal flake-like ZnO microstructures was evaluated by the degradation of methyl orange (MO) under ultraviolet (UV) light irradiation. The results indicated that the best flower-like ZnO microstructure was obtained when the experimental conditions were [Zn2+] = 0.025 mol l−1, [Zn2+]:[NH3·H2O] = 1:1.5, microwave power = 231 W. Under the same reaction conditions, hexagonal flake-like ZnO can be obtained by using sodium hydroxide as precipitant. The MO in aqueous solution was completely eliminated by flower-like ZnO after 120 min of UV light irradiation. Under identical conditions, the degradation of MO in aqueous solution was completely finished within 150 min in the presence of hexagonal flake-like ZnO. The flower-like ZnO sample showed an enhanced photocatalytic activity compared with the hexagonal flake-like ZnO for the MO degradation, which could be attributed to the presence of more active centres and hence can have more opportunities to contact with MO molecules.
Four kinds of x wt.% phosphotungstic acid/silicon carbide (PTA/SiC) photocatalysts were prepared by impregnation method with SiC, 12-phosphotungstic acid (PTA) as raw materials. The structure of samples was characterised by X-ray diffraction, ultraviolet–visible diffuse reflectance spectra, scanning electron microscope. The photocatalytic activity of samples was evaluated by the degradation of rhodamine B (RhB) under a xenon lamp (λ≥420 nm). The results indicate that the photocatalysts not only maintained the SiC structure but also kept the Keggin structure of PTA. The 20 wt.% PTA/SiC exhibited the best photocatalytic degradation efficiency reaching up to 77% for 180 min irradiation, and the photo-degradation rate constant was determined to be 7.82 × 10−3 min−1. In the presence of H2O2, the photocatalytic degradation rate of 20 wt.% PTA/SiC composites was increased to 87%, and the photodegradation reaction rate constant was 7.77 × 10−3 min−1. According to free radical trapping experiments, it is proved that hydroxyl radical (·OH) plays an important role in photocatalysis.
In this study, a typical MXene material, Ti3C2, was selected as a co-catalyst and then integrated with ZnO via a facile hydrothermal strategy. The phase composition, morphology, and photophysical properties of as-prepared samples were investigated by XRD, field emission SEM, ultraviolet–visible spectrophotometer, and fluorescence spectrophotometer, respectively. In addition, the results of the photocatalysis experiment showed that the photocatalytic activity of ZnO can be improved significantly through the hybridisation with Ti3C2, which arises from the inhibition of the photogenerated carriers recombination. Furthermore, the theoretical analysis indicated that the high-quantum efficiency arises from the appropriate Fermi level position of Ti3C2. This work demonstrated that Ti3C2 will show great potential for constructing novel and efficient photocatalysts.
The present work reports the realisation of high-quality crystalline CdS/Mn3O4 (CM) nanocomposites by a simple cost-effective chemical method in air atmosphere. The authors have performed theoretical calculations and experimental analysis in order to understand the synthesised nanocomposites. X-ray diffraction results showed that the CM nanocomposites were cubic and orthorhombic mixed structure which is in good agreement with the theoretical studies. Field emission scanning electron microscopy images of CM confirmed the formation of well distributed nanocomposites. The outcomes of DFT calculations provide results for the bandgap calculation of pure CdS, Mn3O4 and the CM nanocomposites. Photoluminescence studies with interesting visible light absorption demonstrated the great potentiality of the as-synthesised nanocomposites towards photocatalytic applications that could be a detailed research scope for the authors’ future studies.
To investigate the influence of graphene on the photocatalytic activity of bismuth ferrite (BiFeO3), BiFeO3 and flaky BiFeO3@graphene were prepared through the hydrothermal-synthesis process. The as-prepared particles were characterised by XRD, TGA, SEM, X-ray photoelectron spectroscopy, and PL measurements. The results show that the BiFeO3 nanoparticles have a microstructure and homogeneously attached to graphene sheets. Moreover, the flaky BiFeO3@graphene composites exhibited higher photocatalytic efficiency than pure BiFeO3, especially under visible light irradiation. The synergistic effects of graphene and BiFeO3 of composites were proposed to guide the further improvement of their photocatalytic activity.
Bismuth (Bi) micro, nanoparticles are an emerging non-noble metal catalyst, but they are prone to agglomeration due to the large surface energy, which weakens its function and limits its application. Bi nanoparticles were immobilised on activated carbon by the impregnation reduction method to prevent the agglomeration. The prepared material exhibited enhanced photocatalytic efficiency compared to Bi nanoparticles alone. The origin of photocatalytic efficiency enhancement was investigated. It was attributed to the large specific surface area of the composite and more exposed active sites. This research proposes a new strategy for the photocatalytic application of Bi nanoparticles.
Pectin-conjugated CdS/ZnS core/shell nanocrystals were prepared by using a microwave-assisted approach without the addition of any external ligands. The prepared cubic phase CdS/ZnS nanocrystals were uniform and mono-dispersed with sizes of 6–9 nm. The charge and long-chain structure of pectin molecules effectively prevented the aggregation of CdS/ZnS nanocrystals. In addition, pectin molecules have multiple functional groups, such as O–H, C=O, and COO−, which could conjugate with the surface of samples to control the growth of CdS/ZnS nanocrystals. Thermogravimetric analysis provided evidence that the obtained products are inorganic–organic hybrid materials. Based on the analysis of ultraviolet–visible spectra, it was found that the formation of ZnS shell led to a red-shift and an enhancement of absorption of CdS/ZnS nanocrystals compared with that of CdS. Photocatalytic activity of CdS/ZnS nanocrystals was monitored by the degradation of Rhodamine B under visible light irradiation. The presence of ZnS shell inhibited photo-corrosion and photo-dissolution of CdS nanocatalyst, thus resulting in a significant enhancement of photocatalytic activity and stability.
ZnO thin film with different morphologies from seed, array to grass was grown by simple aqueous solution method under room temperature. The morphologies, structure, optical properties and photocatalytic properties of the samples were characterised by transmission electron microscope, scanning electron microscope, X-ray diffraction, fluorescence spectrometer, UV–Vis spectrophotometer and photocurrent response. The results showed that the ZnO arrays and grassy ZnO were both hexagonal wurtzite with uniform distribution and regular growth on the glass substrate. ZnO thin film with different morphologies affected the utilisation efficiency of the ultraviolet light. Multiple light reflections inside the grassy ZnO greatly increase the light efficiency. The methyl blue degradation rate of grassy ZnO photocatalyst was superior under the UV light compared to the other ZnO morphologies. Grassy ZnO showed favourable stability after five cycles. The comparison of the ZnO semiconductor in different dimensions is helpful for further research on other photocatalysts as well as their potential application.
In this study, copper ferrite (CuFe2O4) nanoparticles were successfully prepared and employed as an efficient catalyst for the synthesis of guanidine derivatives through the addition of anilines to N, N-dicyclohexylcarcodiimide under solvent-free conditions. This magnetically retrievable catalyst was well characterised by Fourier transform infrared spectroscopy, X-ray powder diffraction, transmission electron microscopy and field emission scanning electron microscope-energy dispersive X-ray techniques. The catalyst can be readily recovered from the reaction mixture by the use of an external magnet and reused several times without remarkable loss of its catalytic activity.
Electrocatalytic CO2 reduction has offered a promising route for managing the global carbon balance, but presents challenges because of the lack of highly efficient and low-cost electrocatalyst. Compared with the dispersity of metal active sites, the porous structure of the substrate is more significant for the catalytic performance and the design and fabrication of substrate are often the key points and difficulties for electrocatalysts. Herein a facile method to disperse Ni active sites on nitrogen-doped carbon aerogels with high surface area and porosity is reported. Firstly, hydrophilic polysaccharides were prepared by the hydrothermal process of glucose, followed by ultrasonic mixing with Ni complex and melamine. Secondly, calcination was used to increase the surface area and conductivity of the freeze-dried mixture. The Ni/N-C catalyst exhibited good activity with a Faradaic efficiency for CO production of about 95% and a current density of ∼8 mA cm−2 at an overpotential of 750 mV. The result presents helpful guidelines for the rational design and accurate modulation of low-cost and efficient catalysts.
Gold nanoparticles (AuNPs) possess colourful light-scattering properties due to different composition, size and shape. Their unique physical, optical and chemical properties coupled with advantages, have increased the scope of anisotropic AuNPs in various fields. This study reports a green methodology developed for the synthesis of anisotropic AuNPs. The aqueous extracts of Alternanthera sessilis (PGK), Portulaca oleracea (PAK) and Sterculia foetida (SF) with gold ions produced violet, purple and pink coloured AuNPs, respectively, under sonication and room temperature methods revealing the formation of different shapes of AuNPs. The results of TEM analysis of AuNPs confirmed the formation of triangular plate AuNPs of the size 35 nm for PAK extract. Spherical-shaped AuNPs (10–20 nm) were obtained using an extract of PGK. SF extract produced rod, hexagon, pentagon-shaped AuNPs and nanorice gold particles. The cell viability studies of the PGK, PAK and SF-mediated AuNPs on MCF-7 cell lines by MTT assay revealed the cytotoxic activity of AuNPs to depend on the size, shape and the nature of capping agents. The synthesised AuNPs significantly inhibited the growth of cancer cells (MCF-7) in a concentration-dependent manner. The size and shape of these anisotropic AuNPs also reveal its potency to be used as sensors, catalysis, photothermal and therapeutic agents.
Carbon quantum dots (CQDs) decorated Bi2WO6 nanocomposites were successfully synthesised by a facile hydrothermal method. The prepared samples were characterised by the XRD, FESEM, TEM, XPS, UV–vis DRS, photocurrent and photoluminescence (PL) techniques. The DRS, photocurrent, PL spectra measurements reveal that the introduction of CQDs could broaden the absorption edge and accelerate the separation and transportation efficiency of carriers. Moreover, a reasonable charge transfer approach was given out based on the calculated work function and the differential charge difference. The CQDs/Bi2WO6-2 sample provides the optimal activity for photodegradation of CIP under simulated sunlight irradiation. It is hopeful that this work not only gives a reference for the design of CQDs/Bi2WO6 composites, but also provides some mechanistic insights into enhanced photoactivity.
Novel triclinic bismuth oxide (ω-Bi2O3) microcrystals with a pyramid-like shape were successfully synthesised by a facile hydrothermal method. The effects of potassium sodium tartrate (KNaC4H4O6·4H2O) concentration and the reaction time on the morphology were investigated, respectively. The experimental results showed that the tartrate (C4H4O6 2–) ions were responsible for the crystal growth of pyramid-like ω-Bi2O3 at the same reaction time. The photocatalytic activity of ω-Bi2O3 pyramids was evaluated by degrading methyl orange under the visible-light irradiation, revealing the ω-Bi2O3 pyramids exhibited outstanding photocatalytic activity due to its suitable bandgap energy.