Facile one-pot synthesis of Mg-doped g-C3N4 for photocatalytic reduction of CO2

Graphitic carbon nitride (g-C₃N₄) has attracted wide attention due to its potential in solving energy and environmental issues. However, rapid charge recombination and a narrow visible light absorption region limit its performance. In our study, Mg-doped g-C₃N₄ was synthesized through a facile one-pot strategy for CO₂ reduction. After Mg doping, the light utilization efficiency and photo-induced electron–hole pair separation efficiency of the catalysts were improved, which could be due to the narrower band gap and introduced midgap states. The highest amounts of CO and CH₄ were obtained on Mg-CN-4% under ultraviolet light illumination, which were about 5.1 and 3.8 times that of pristine g-C₃N₄, respectively; the yield of CO and CH₄ reached 12.97 and 7.62 μmol g⁻¹ under visible light irradiation. Our work may provide new insight for designing advanced photocatalysts in energy conversion applications.

Graphitic carbon nitride (g-C₃N₄) has attracted wide attention due to its potential in solving energy and environmental issues.     

Facile synthesis of nitrogen-defective g-C3N4 for superior photocatalytic degradation of rhodamine B

Developing a new photocatalyst for fast and highly efficient organic dye degradation plays an essential role in wastewater treatment. In this study, a photocatalyst graphite phase carbon nitride (g-C₃N₄) containing nitrogen defects (CN) is reported for the degradation of rhodamine B (RhB). The porous g-C₃N₄ photocatalyst is facilely synthesized through a polycondensation method and then characterized by X-ray diffraction (XRD), infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), N₂ isotherm adsorption line, and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the g-C₃N₄ is evaluated through the degradation of RhB under visible light irradiation. The results show that photocatalytic activity of the nitrogen-defective g-C₃N₄ can be improved by optimizating washing conditions, including washing temperature, washing dosage, drying time, and drying temperature. With the prepared nitrogen-defective g-C₃N₄, decolourization of RhB is able to be completed within 20 minutes, in which the degradation rate is 1.7 times higher than that of bulk g-C₃N₄. Moreover, the nitrogen-defective g-C₃N₄ has high stability and reusability in the degradation of RhB. Photocatalytic degradation mechanism investigations by ultraviolet-visible absorption spectroscopy, radical trapping experiments and high-performance liquid chromatography (HPLC) reveal that RhB achieved complete mineralization through the photocatalytic degradation reaction mediated by superoxide radicals (˙O₂⁻). This work thus provides a new approach for the preparation of photocatalysts for organic pollutants treatment in wastewater samples.

Nitrogen-defective g-C₃N₄ is synthesized and characterized as the photocatalyst for degradation of organic dyes, such as rhodamine B, in wastewater.     

Facile synthesis of g-C3N4 with various morphologies for application in electrochemical detection

In the present study, g-C₃N₄ with various morphologies was successfully synthesized via a variety of facile in situ methods. The as-prepared products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray diffraction (XRD). The results obtained using square wave anodic stripping voltammetry (SWASV) showed that when g-C₃N₄ was applied as an electrochemical sensor, it exhibited excellent sensitivity and selectivity for the detection of heavy metal ions including Pb(ii), Cu(ii) and Hg(ii). Compared to nanoporous graphitic carbon nitride (npg-C₃N₄) and g-C₃N₄ nanosheet-modified glass carbon electrode (GCE), g-C₃N₄ successfully realized the individual and simultaneous detection of four target heavy ions for the first time. In particular, g-C₃N₄ displayed significant electrocatalytic activity towards Hg(ii) with a good sensitivity of 18.180 μA μM⁻¹ and 35.923 μA μM⁻¹ under the individual and simultaneous determination conditions, respectively. The sensitivity for simultaneous determination was almost 2 times that of the individual determination. Moreover, the fabricated electrochemical sensor showed good anti-interference, stability and repeatability; this indicated significant potential of the proposed materials for application in high-performance electrochemical sensors for the individual and simultaneous detection of heavy metal ions.

In the present study, g-C₃N₄ with various morphologies was successfully synthesized via a variety of facile in situ methods.     

Pulse electrochemical synthesis of polypyrrole/graphene oxide@graphene aerogel for high-performance supercapacitor

A novel electroactive polypyrrole/graphene oxide@graphene aerogel (PGO@GA) was synthesized for the first time by pulse electropolymerization. The off-time in this technique allows polypyrrole (PPy) to go through a more stable structural arrangement, meanwhile its electronic transmission performance is enhanced by immobilizing graphene oxide between PPy chains. Moreover, graphene aerogel provides a three-dimensional structure with high conductivity to protect PPy from swelling and shrinking during the capacitive testing. Under these synergistic effects, PGO@GA presents exceptional capacitive performances including high specific capacitance (625 F g⁻¹ at 1 A g⁻¹), excellent rate capability (keeping 478 F g⁻¹ at 15 A g⁻¹ with retention rate of 76.5%), and excellent cycling life (retaining 85.7% of its initial value when cycling 5000 times at 10 A g⁻¹). Therefore, the strategy adopted by this research provides a good reference for preparing other PPy-based electrode materials applied in the fields of catalysis, sensing, adsorption and energy storage.

The as-prepared polypyrrole/graphene oxide@graphene aerogel by pulse electropolymerization technique presents excellent capacitive performance.

Polypyrrole (PPy), a widely-used conducting polymer, holds huge application potential in sewage disposal,¹ extraction of precious metals,² catalysts,³ sensing⁴ and energy storage,⁵ owing to its advantages including superior biocompatibility, relatively high conductivity, high electrochemical activity and low preparation cost.⁶ Together with its excellent pseudocapacitive properties, PPy usually acts as an outstanding electrode material applied in the field of supercapacitors. However, there still exist some defects in pure PPy because its chains suffer from serious swelling and shrinking during the charge–discharge process, which in turn severely weakens the rate capability and cycling life of supercapacitors.⁷Pulse electropolymerization, compared with the method of constant potential⁸ or galvanostatic deposition,⁹ can regulate on-off time, pulse cycles and work potential to make pyrrole monomers continually polymerized into PPy on new active sites, and meanwhile to allow newly-formed PPy have enough time of experiencing structural rearrangement to improve its structural stability and electrochemical activity.¹⁰ For the sake of further overcoming the intrinsic flaws of pure PPy and developing its potentials, up to now, various PPy-based composites have been designed. For instance, some groups have realized the improvement of electronic transport property of PPy^11,12 by incorporating graphene oxide with large-size anion nature into PPy chains. Singu and Yoon developed a novel ternary composite (GO–PPy–Ag)¹³ exhibiting high specific capacitance (277.5 F g⁻¹ at 2 A g⁻¹) and superior cycle life (keeping 93% after cycling 5000 charge–discharge at 2 A g⁻¹). Apart from these cases, graphene, owing to its exceptional conductivity, large theoretical specific surface area and excellent chemical stability,¹⁴ has always been the most acceptable material employed to functionalize PPy for integrating their respective advantages. For instance, Ma et al.¹⁵ synthesized polypyrrole/bacterial cellulose/graphene by a combination of in situ polymerization and filtering method, and the obtained nanomaterial exhibited a high areal capacitance of 3.66 F cm⁻² at 1 mA cm⁻². Nevertheless, the inherent advantages of graphene are far from being full developed owing to serious restacking of graphene sheets caused by the enhanced π–π interaction during chemical or electrochemical reduction of GO.¹⁶Graphene aerogel, as one emerging material, is synthesized by self-assembly of graphene sheets in different crosslinking ways.¹⁷ The crosslinks not only restrain the restacking of graphene sheets efficiently but also initiate the formation of hierarchical pores that can shorten transport route of ions. Together with its excellent conductivity, graphene aerogel can serve as an excellent conductive matrix¹⁸ to support the electrochemical deposition of PPy.In this research, polypyrrole/graphene oxide@graphene aerogel (PGO@GA) nanocomposite was designed and constructed, which achieves a more enhanced capacitive performance than PPy owing to the modification of GO and graphene aerogel. The structure–activity relationship between components, morphologies and capacitive performances for this ternary composite was discussed on the basis of a series of structural characterization and electrochemical test.The synthesis route of PGO@GA is illustrated in Fig. 1. First, the working electrode is prepared by coating method. Then it is immersed in electrolyte containing pyrrole monomer, GO and KCl (acting as supporting electrolyte). As is well known, GO dissolved in aqueous solution always carries negative charge owning to ionization of carboxyl and phenolic hydroxyl groups on GO.¹⁹ At work potential, pyrrole monomers are oxidized into PPy whose chains carry positive electricity to attract negatively charged GO onto them. At the subsequent open circuit potential, the circulating current is cut off so that the oxidation polymerization reaction stops and meanwhile the relatively long off-time promotes diffusion of pyrrole monomers towards reactive boundary layer on electrode surface to form new active sites, where pyrrole monomers constantly grow into PPy at the next work potential, accompanied with the continuous doping of ionized GO sheets. Going through such a recurrent pulse electropolymerization process, PGO@GA is formed.Open in a separate windowFig. 1Pulse electropolymerization technique for synthesis of PGO@GA. Fig. 2 exhibits the FTIR spectra of GO, PPy, PGO and PGO@GA. For GO, the bands at 1731, 1610 and 1056 cm⁻¹ correspond to stretching vibration of C O, graphitic C C and C–O–C (alkoxy group), respectively.²⁰ As for PPy, the bands at 1541 and 1460 cm⁻¹ correspond to the symmetric and asymmetric stretching vibrations of pyrrole ring.²¹ The band located at 1295 cm⁻¹ is related with the in-plane vibration of C–H while that at 1037 cm⁻¹ is attributed to C–H deformation vibration.^22,23 The bands at 963 and 773 cm⁻¹ indicate the formation of polymerized pyrrole, meanwhile, the bands at 1187 and 910 cm⁻¹ imply the doping state of PPy.²⁴ It is worth noting that all the bands of PPy also appear in PGO and PGO@GA, proving the introduction of PPy. Apart from that, the band ascribed to the C O group of GO downshifts to 1700 cm⁻¹ for PGO and PGO@GA because of the π–π interaction and the hydrogen bonding produced between GO layers and aromatic polypyrrole rings,²⁵ proving that carboxyl group plays an important role when GO is immobilized into PPy chains.Open in a separate windowFig. 2FTIR spectra of GO, PPy, PGO and PGO@GA.It can be observed from SEM images, as shown in Fig. 3(a–c), that GA exhibits three-dimensional network structure consisting of graphene sheets with highly wrinkled and chiffon-like features. As shown in Fig. S1 and S2,^† the morphology and specific capacitance of PPy vary as a function of pulse cycle. It can be observed that PPy prepared at pulse cycles of 1000 obtains the highest specific capacitance (453 F g⁻¹), owing to its smooth micromorphology (Fig. 3d–f) that facilitates the electron mobility,²⁶ and the mass of PPy deposited on carbon cloth (19.2 mg) is about 4.8 mg. By contrast, the mass of PPy at pulse cycles of 500, 1500, 2000, 2500 and 3000 achieves 2.6, 9.6, 10.6, 14.9 and 17.8 mg respectively. Therefore, it can be evaluated that the PPy film gets much thicker as the increase of pulse cycles and pulse cycles are set as 1000 to prepare PGO and PGO@GA. Compared with pure PPy, PGO obtains a smoother microstructure (Fig. 3g–i) owing to the introduction of GO, which endows PGO with higher electrochemical activity than PPy. It can be observed from Fig. 3j–l that PGO@GA exhibits a coral-like structure, on which flat polymer layers are distributed.Open in a separate windowFig. 3SEM images of samples at different magnifications. (a–c) GA, (d–f) PPy, (g–i) PGO, (j–l) PGO@GA.At excitation wavelength of 532 nm, the G peak of single and double layers of graphene is located at 1614 and 1608 cm⁻¹ respectively.²⁷ Based on interpolation method,²⁸ the stacked graphene layers of PGO@GA, whose G peak is at 1584 cm⁻¹ (Fig. S3b^†), are about 6. As is well known, thickness of a single layer of graphene is around 1 nm,²⁹ therefore, the thickness of stacked graphene in void pore wall is ∼6 nm. It can be tested from Fig. 3l that thickness of void pore wall is ∼14 nm, accordingly, the thickness of PPy deposited on GA is about 8 nm.The structures of GO, PPy, PGO and PGO@GA were analyzed by XRD and Raman. Two peaks centered at 2θ = 10.9° and 21.7° correspond to the (001) plane and (002) plane of GO, respectively (Fig. S3a^†). The broad peaks located at 2θ = 25.3° (3.5 Å) for PPy, PGO and PGO@GA are associated with the closest distance between the planar aromatic rings of pyrrole, like face-to-face pyrrole rings.^30,31 Except for PPy, diffraction peak for (001) crystal face of GO at 2θ = 10.9° also appears on PGO and PGO@GA, indicating the introduction of GO into these two materials.In the Raman spectra (Fig. S3b^†), as for PPy, the peak located at 1571 cm⁻¹ is due to C C backbone stretching.³² The double peaks situated at 1230 and 1320 cm⁻¹ are attributed to the ring-stretching mode of PPy and another double peaks at 1041 and 979 cm⁻¹ mainly come down to the C–H in-plane deformation.³³ However, these peaks belonging to PPy disappears in PGO and PGO@GA composites except for the slightly up-shifted D band approaching the peak of PPy at 1320 cm⁻¹. It can be speculated that the immobilization of GO into PPy chains results in the change in molecular vibration and rotation of PPy.The elemental constituents of samples were analyzed using XPS (Fig. S4^†). It is worth noting that the atomic percentage content of oxygen increases successively from PPy, PGO to PGO@GA (Fig. S4a^†), which is attributed to the functionalization of PPy by GO and GA. The relatively high oxygen content in PPy mainly results from its molecular conformation optimization during the pulse electropolymerization process,²⁶ which facilitates the diffusion of water to form hydroxyl radical for nucleophilic attack towards PPy. What is more important is that the high oxygen contents endow these materials with excellent hydrophilicity favourable for lowering the transmission resistance of electrolyte and thus forming large reactive interface area. It is observed from Fig. S4b^† that only pyrrolic N³⁴ exists, accompanied with bonding energy differences among them, which can be explained by the generated electron transfer between PPy, GO and GA. The elemental mappings reveal that carbon, nitrogen, and oxygen elements coexist and are distributed over the sheets (Fig. S5^†), demonstrating the hybrid structure.The capacitive performances of PPy, PGO and PGO@GA were investigated in 1.0 M KCl by using cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS). It can be seen from Fig. 4a that CV curves of PPy, PGO and PGO@GA at 5 mV s⁻¹ all exhibit quasi-rectangular shapes, demonstrating ideal electrical double-layer capacitor (EDLC) behaviors at electrode–electrolyte interface.³⁵ Apart from that, the closure area of CV curve for PPy, PGO and PGO@GA increases successively, indicating elevated specific capacitance in turn. That is due to the following reasons: (1) the negatively charged GO immobilized into PPy chains must be balanced by cation ingression from electrolyte, which contributes to a higher current density in the negative potential region²⁵ and the involved reaction mechanism can be described as: PPy⁺/GO⁻ + K⁺ +e ↔ PPy⁰/GO⁻/K⁺;³⁶ (2) the coral-like network with superior conductivity for GA not only shortens transmission path of ions in electrolyte and accelerates electron transfer but also protects PPy from structural deformation.Open in a separate windowFig. 4Capacitive properties of samples in 1.0 M KCl: (a) CV curves at 5 mV s⁻¹; (b) GCD profiles at 1 A g⁻¹; (c) capacitance values at current densities ranging from 1 to 15 A g⁻¹; (d) Nyquist plots of PPy, PGO, PGO@GA, and the equivalent circuit used to fit EIS results (inset); (e) cycling stability of PPy, PGO, PGO@GA at a current density of 10 A g⁻¹.Similar tendency can be also seen from Fig. 4b. All GCD curves present quasi-isosceles triangle, indicating that the capacitance mainly comes from the EDLC properties of materials in neutral electrolyte. The capacitance value for PPy, PGO and PGO@GA at 1 A g⁻¹ achieves 453, 514 and 625 F g⁻¹, respectively.The capacitance for PPy, PGO and PGO@GA corresponding to the current densities ranging from 1 to 15 A g⁻¹ was investigated and the results are shown in Fig. 4c. It can be observed that specific capacitance of PGO@GA still achieves 478 F g⁻¹ even at high current density of 15 A g⁻¹ with a relatively high capacitance retention rate of 76.5%, which is obviously higher than those of PGO (58.7%) and PPy (25.2%), demonstrating that the synergistic effect among GO, PPy and GA promotes the rate capability of PGO@GA.EIS analysis of PPy, PGO and PGO@GA was conducted to detect their charge transfer resistance and ion diffusion rate, and the results are presented in Fig. 4d. Based on the equivalent circuit, the intercept with the real impedance axis in the high-frequency region represents equivalent series resistance R_s, including contact resistance, intrinsic resistance of electrode materials and solution resistance.³⁷ The diameter of the semicircle in medium-frequency region symbolizes charge-transfer resistance (R_ct). As proved in M. Deng et al.''s reports,¹¹ electron transmission ability of PPy is improved owing to the introduction of GO between PPy chains. Moreover, X. Du et al.''s research²⁶ also demonstrates that point based on the reduced R_ct. Therefore, similar conclusion can be drawn from the fitted results illustrated in Fig. 4d that R_s and R_ct values for PGO and PGO@GA get lower than those of PPy after PPy goes through the functional modification of GO and GA.The Warburg region refers to the section of curve with 45° slope, corresponding to the intermediate frequency range. The shorter the frequency range gets, the better ion diffusion capability the material exhibits. Therefore, it can be concluded from the fitted results in Fig. 4d that the modification of GO, GA and pulse regulation for PPy realizes the optimum ion diffusion for PGO@GA.In addition, compared with the curve of PPy and PGO in low-frequency region, that for PGO@GA is closer to parallel with imaginary axis, which implies its more ideal EDLC behaviors.It can be seen from the cyclic stability test (Fig. 4e) that the capacitance retention for PGO@GA achieves 85.7% even undergoing 5000 cycles at 10 A g⁻¹, higher than that for PPy (38.5%) and PGO (59.2%).Most of the reported materials listed in Table S1^† are prepared by non-pulse deposition techniques. These electrode materials fail to achieve high specific capacitance as well as excellent capacitance stability simultaneously, which is mainly attributed to the serious swelling and shrinking of polypyrrole during charge–discharge process. By contrast, a combination of pulse regulation, modification of GO and protection of GA towards PPy endows PGO@GA with smooth porous microstructure and enhances structural stability of PPy, which facilitates electron mobility and electrolyte transport. Therefore, PGO@GA enjoys higher capacitance stability even after 5000 charge–discharge cycles at the high current density of 10 A g⁻¹, besides, the material also obtains a higher mass specific capacitance at 1 A g⁻¹.It can be concluded from all the above electrochemical performance test results that PGO@GA electrode holds optimum capacitance performance, which is attributed to the following reasons: (1) during pulse electropolymerization, PPy experiences more stable structural rearrangement to endow it with improved electrochemical activity; (2) large-sized GO with anionic attribute is immobilized into PPy to optimize its electron transport property and structural stability; (3) GA provides three-dimensional network with good conductivity supporting anisotropic deposition of pyrrole monomer and GO, which not only generates large number of active sites of electrochemical reaction but shortens ion transport paths and inhibit the swelling and shrinking of polypyrrole also during charge–discharge process.In conclusion, the synthetic PGO@GA by pulse electropolymerization technique exhibits high specific capacitance (625 F g⁻¹) at 1 A g⁻¹ and still retains 478 F g⁻¹ even at a high current density of 15 A g⁻¹ with superior capacitance retention rate of 76.5%. Moreover, excellent cycling life (retaining 85.7% of its initial value when cycling 5000 times at 10 A g⁻¹) for PGO@GA is also obtained. The outstanding capacitance behavior benefits from multiplexed conduction channel from GA and the enhanced structural stability and electrochemical activity of PPy. It is expected that the improved modification strategy for PPy provided by this research will be a good reference to synthesize other types of PPy-based nanomaterial by regulating the categories of anions and conductive matrix to realize applications in established fields.     

AgBr/g-C3N4 nanocomposites for enhanced visible-light-driven photocatalytic inactivation of Escherichia coli

Visible-light-driven photocatalytic disinfection is highly desired for water treatment due to its advantages such as wide applicability and being free of disinfection byproducts. In this study, AgBr/g-C₃N₄ hybrid nanocomposites were evaluated as photocatalysts under visible light irradiation for water disinfection using Escherichia coli as a model pathogen. The physicochemical and photo-electrochemical properties of the photocatalyst were systematically characterized using advanced techniques including scanning electron microscopy (SEM), transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), UV-visible diffuse reflectance spectra (DRS), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) spectra and electron spin resonance (ESR) spectroscopy. The inactivation mechanism of E. coli was systematically investigated by monitoring the morphology change of the bacteria and analyzing the role of reactive species. The optimized AgBr/g-C₃N₄ hybrid photocatalyst exhibited remarkably enhanced visible-light-driven photocatalytic disinfection performance towards E. coli over that of pure g-C₃N₄ and AgBr under visible light, which could completely inactivate 10⁷ cfu mL⁻¹E. coli in 90 min. Quenching studies indicated that h⁺ is the main reactive species responsible for inactivating E. coli. The mechanism study revealed a Z-scheme charge transfer mechanism between AgBr and g-C₃N₄. The g-C₃N₄ could effectively trap the photogenerated conduction band electrons of AgBr via a Z-scheme type of route, thus significantly promoting the electron–hole separation. The trapping of electrons by g-C₃N₄ could facilitate h⁺ accumulation, which accounts for the better disinfection performance of AgBr/g-C₃N₄ compared to AgBr and g-C₃N₄.

AgBr/g-C₃N₄ can efficiently inactivate E. coli under the irradiation of visible light.     

Porous g-C3N4 covered MOF-derived nanocarbon materials for high-performance supercapacitors

Supercapacitors with high power density and long cycle life have shown great potential in energy storage supply for modern electronic devices. Among the component parts of supercapacitors, electrode materials with high electrical conductivity, large surface area and porosity are critical to the energy storage performances of devices. Here, we report a porous g-C₃N₄ covered MOF-derived nanocarbon material with large specific surface area and high nitrogen doping level as an electrode material for supercapacitors. The large surface area provides high capacity for ion accommodation during electrochemical processes, and the high nitrogen doping facilitates electron and ion transport with extra pseudocapacitance. The supercapacitor based on the as-synthesized material delivers a high specific capacity of 106 F g⁻¹ at current density of 1 A g⁻¹ as well as good rate capability. Furthermore, the device presents good cycling stability with capacitance retention of 91% even after 10 000 cycles at 1 A g⁻¹ under 0.8 V. This study presents a new insight into the design of nanocomposite materials with high energy storage capability and will accelerate the practical application of supercapacitors in future.

Here, we report a porous g-C₃N₄ covered MOF-derived nanocarbon material with large surface area and high nitrogen doping for supercapacitors.     

Facile synthesis of an all-in-one graphene nanosheets@nickel electrode for high-power performance supercapacitor application

We report a facile and novel approach for the fabrication of all-in-one supercapacitor electrodes by in situ electrochemical exfoliation of flexible graphite paper (FGP) on a nickel collector. The binder-free three dimensional (3D) graphene nanosheets@Ni (GNSs@Ni) supercapacitor electrodes exhibit a high specific capacitance of 196.4 F g⁻¹ and 36.2 mF cm⁻², respectively, at a scan rate of 50 mV s⁻¹. Even at the high scan rate of 2500 mV s⁻¹ the specific capacitance of the capacitor still shows a retention of 85.6% (168 F g⁻¹, 31 mF cm⁻²). Meanwhile, the as-prepared electrode offers excellent cycling performance with 91.5% capacitance retention after 100 000 charging–discharging cycles even at the high current density of 11 A g⁻¹. Such high rate capability, specific capacitance and exceptional cycling ability of the GNSs@Ni electrode are attributed to the all-in-one architecture which provides unique properties including high electrical conductivity, large specific surface area and excellent electrochemical stability. We anticipate that these results will shed light on new strategies to synthesize high-performance hybrid nanoarchitectures electrodes using the prepared graphene nanosheets as the support, which offers great potential in energy storage devices and electrochemical catalysis applications.

GNSs@Ni electrode has a high current density, and the C_m and C_s are estimated to be 196.4 F g⁻¹ and 36.2 mF cm⁻².     

Correction: Facile preparation of novel quaternary g-C3N4/Fe3O4/AgI/Bi2S3 nanocomposites: magnetically separable visible-light-driven photocatalysts with significantly enhanced activity

Correction for ‘Facile preparation of novel quaternary g-C₃N₄/Fe₃O₄/AgI/Bi₂S₃ nanocomposites: magnetically separable visible-light-driven photocatalysts with significantly enhanced activity’ by Anise Akhundi et al., RSC Adv., 2016, 6, 106572–106583. DOI: 10.1039/C6RA12414C.

The authors regret that incorrect images were used in Fig. 2i (page 106575) and Fig. 3b (page 106576). The correct images are shown below.Fig. 2i. EDX mapping of the g-C₃N₄/Fe₃O₄/AgI/Bi₂S₃ (30%) nanocomposite.Fig. 3b TEM image of the g-C₃N₄/Fe₃O₄/AgI/Bi₂S₃ (30%) nanocomposite.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Synthesis and characterization of CuO@S-doped g-C3N4 based nanocomposites for binder-free sensor applications

This study presents the simultaneous exfoliation and modification of heterostructured copper oxide incorporated sulfur doped graphitic carbon nitride (CuO@S-doped g-C₃N₄) nanocomposites (NCs) synthesized via chemical precipitation and pyrolysis techniques. The results revealed that the approach is feasible and highly efficient in producing 2-dimensional CuO@S-doped g-C₃N₄ NCs. The findings also showed a promising technique for enhancing the optical and electrical properties of bulk g-C₃N₄ by combining CuO nanoparticles (NPs) with S-doped g-C₃N₄. The crystallite and the average size of the NCs were validated using X-ray diffraction (XRD) studies. Incorporation of the cubical structured CuO on flower shaped S-doped-g-C₃N₄ was visualized and characterized through XRD, HR-SEM/EDS/SED, FT-IR, BET, UV-Vis/DRS, PL, XPS and impedance spectroscopy. The agglomerated NCs had various pore sizes, shapes and nanosized crystals, while being photo-active in the UV-vis range. The synergistic effect of CuO and S-doped g-C₃N₄ as co-modifiers greatly facilitates the electron transfer process between the electrolyte and the bare glassy carbon electrode. Specific surface areas of the NCs clearly revealed modification of bulk S-doped g-C₃N₄ when CuO NPs are incorporated with S-doped g-C₃N₄, providing a suitable environment for the binder-free decorated electrode with sensing behavior for hazardous pollutants. This was tested for the preparation of a 4-nitrophenol sensor.

This study presents the simultaneous exfoliation and modification of heterostructured copper oxide incorporated sulfur doped graphitic carbon nitride (CuO@S-doped g-C₃N₄) nanocomposites synthesized via chemical precipitation and pyrolysis techniques.     

g-C3N4/CuO and g-C3N4/Co3O4 nanohybrid structures as efficient electrode materials in symmetric supercapacitors

Metal oxide dispersed graphitic carbon nitride hybrid nanocomposites (g-C₃N₄/CuO and g-C₃N₄/Co₃O₄) were prepared via a direct precipitation method. The materials were used as an electrode material in symmetric supercapacitors. The g-C₃N₄/Co₃O₄ electrode based device exhibited a specific capacitance of 201 F g⁻¹ which is substantially higher than those using g-C₃N₄/CuO (95 F g⁻¹) and bare g-C₃N₄ electrodes (72 F g⁻¹). At a constant power density of 1 kW kg⁻¹, the energy density given by g-C₃N₄/Co₃O₄ and g-C₃N₄/CuO devices is 27.9 W h kg⁻¹ and 13.2 W h kg⁻¹ respectively. The enhancement of the electrochemical performance in the hybrid material is attributed to the pseudo capacitive nature of the metal oxide nanoparticles incorporated in the g-C₃N₄ matrix.

Comparison of electrochemical performance of symmetric supercapacitors based on g-C₃N₄/CuO and g-C₃N₄/Co₃O₄ electrodes.     

Black titania nanotubes/spongy graphene nanocomposites for high-performance supercapacitors

A simple method is demonstrated to prepare functionalized spongy graphene/hydrogenated titanium dioxide (FG-HTiO₂) nanocomposites as interconnected, porous 3-dimensional (3D) network crinkly sheets. Such a 3D network structure provides better contact at the electrode/electrolyte interface and facilitates the charge transfer kinetics. The fabricated FG-HTiO₂ was characterized by X-ray diffraction (XRD), FTIR, scanning electron microscopy (FESEM), Raman spectroscopy, thermogravimetric analysis (TGA), UV-Vis absorption spectroscopy, and transmission electron microscopy (TEM). The synthesized materials have been evaluated as supercapacitor materials in 0.5 M H₂SO₄ using cyclic voltammetry (CV) at different potential scan rates, and galvanostatic charge/discharge tests at different current densities. The FG-HTiO₂ electrodes showed a maximum specific capacitance of 401 F g⁻¹ at a scan rate of 1 mV s⁻¹ and exhibited excellent cycling retention of 102% after 1000 cycles at 100 mV s⁻¹. The energy density was 78.66 W h kg⁻¹ with a power density of 466.9 W kg⁻¹ at 0.8 A g⁻¹. The improved supercapacitor performance could be attributed to the spongy graphene structure, adenine functionalization, and hydrogenated titanium dioxide.

A simple method is demonstrated to prepare functionalized spongy graphene/hydrogenated titanium dioxide (FG-HTiO₂) nanocomposites as interconnected, porous 3-dimensional (3D) network crinkly sheets.     

Facile synthesis and optical properties of colloidal quantum dots/ZnO composite optical resonators

We present a novel colloidal quantum dot (CQD)/ZnO whispering gallery mode microcavity composite. The whispering gallery mode emission of the CQDs induced by the ZnO microcavity is realized. The resonant properties of the composite optical cavities are systematically investigated, and the obtained results are supported by finite element method simulations. The work presents a new research platform to study light–matter interactions in such a composite microcavity.

We present a facile method of incorporating CdSe/Zn_xCd_1−xS CQDs onto the surface of a ZnO WGM optical microcavity. The whispering gallery mode emission of the CQDs induced by the ZnO microcavity is directly observed.

Quantum dots (QDs) feature a quantized energy structure, attracting considerable attention due to their narrow-linewidth emission spectra, high quantum efficiencies, and broad-energy-range size-tunable band gaps.^1,2 In this research field, great efforts have been devoted to the studies of the combination of QDs with optical microcavities, which is very important both for fundamental research on light–matter interactions and for optics- and photonics-related applications. Most of the previously described composite systems feature a distributed Bragg reflector (DBR) structure and self-assembled QDs, which have allowed great progress in the development of single-photon sources,^3,4 photodetectors,^5,6and cavity lasers.^7,8 However, the above QDs (used as gain materials in these composites) were mostly based on III–V semiconductors prepared by molecular beam epitaxy (MBE)⁹ or metal-organic chemical vapor deposition (MOCVD).^10,11 Moreover, DBR-structured microcavities are usually fabricated using MBE, MOCVD, or sputtering, additionally requiring the utilization of electron beam lithography (EBL) and other nano-etching technologies.^12–16 Thus, these sophisticated and expensive fabrication techniques and limited material availability are not conducive to the development of this research field.In contrast, colloidal quantum dots (CQDs) exhibit the advantages of high optical stability, solution processability, and emission wavelength tunability,^17,18 being well suited for use in composite microcavities. However, the hybridization of CQDs is difficult, with the main method used for this purpose also being rather complex, featuring the insertion of a CQDs layer into the DBR structure by spin coating.¹⁹ The methods like epitaxial growth have been used to synthesize and incorporate CQDs into a photonic crystal distributed feedback (PC-DFB) optical cavity,²⁰ or fabricate on-chip microdisk laser.²¹ They all require expensive equipment, e.g. plasma-enhanced chemical vapor deposition (PECVD) or RF frequency sources, and the process of them are also relatively complex. In addition, alkyl modification and drop-coating also have been used to attach CQDs to silica microbeads²² and submicron scale grating structures²³ showing good composite effect. Nano/microstructure optical cavities with regular geometric configurations are another important class of microcavities,^24–26 attracting growing interest due to their ease of synthesis, high tunability, and excellent optical confinement effect. Among these cavities, ZnO microrod hexagonal whispering-gallery-mode (WGM) microcavities are the ones most extensively studied,^27–31 allowing light confinement due to multiple total internal reflection (TIR) at resonator boundaries and thus enabling effective control of light–matter interaction. This control is essential for both fundamental physics research in the field of cavity quantum electrodynamics and the development of cavity-based optoelectronic devices, and it is therefore believed that the formation of CQDs/microcavity composites will promote further progress in the optical modulation of CQDs.Herein, we present a facile method of incorporating CdSe/Zn_xCd_1−xS CQDs onto the surface of a ZnO hexagonal microrod WGM optical cavity. The modulated emission of the CQDs induced by the ZnO microrod cavity was observed. And, the coupling properties of the CQDs/microcavity composite system have been also studied at room temperature. A whispering gallery mode (WGM) was identified by calculations based on the TIR model and further confirmed by Finite Element Method (FEM) simulations. Furthermore, the resonant properties in relation to the CQDs were studied in detail. Notably, we also demonstrate the occurrence of energy transfer between CQDs and the ZnO microcavity. Thus, our work describes a simple method of investigating optical property coupling between CQDs and nano/microstructure optical cavities.Single-crystalline ZnO microrods were grown on a silicon (Si) substrate in a horizontal tube furnace (with no catalysts, carrier gases, low pressure, or templates used) utilizing a reduction–oxidation method similar to that described in our previous report.³² Core/shell CdSe/Zn_xCd_1−xS CQDs were prepared as described elsewhere,³³ purified by centrifugation and decantation using a toluene/ethanol mixture as a solvent, and redispersed in toluene. The CQDs/ZnO microrod composite was prepared by dropcasting the above dispersion onto ZnO microrods deposited on a clean Si wafer to form a thin CQDs film, with the corresponding photoluminescence (PL) spectra recorded after solvent evaporation. The morphology, composition, and microstructures of the obtained samples were characterized by field emission scanning electron microscopy (FE-SEM, Zeiss Auriga S40), high-resolution transmission electron microscopy (HRTEM, JEOL JEM-2010), and energy-dispersive spectroscopy (EDS). The optical properties of a chosen individual ZnO microrod were determined by confocal micro-photoluminescence spectrometry (JY LabRAM HR800 UV) using a 325 nm He–Cd laser as an excitation source. FEM simulations were carried out using commercial finite element software (COMSOL Multiphysics). Fig. 1(a) shows atypical SEM image of as-synthesized ZnO microrods. A large quantity of rod-like microstructures with smooth surface was produced on the Si wafer. Most of the microrods have diameters in the range of 2–5 μm and lengths exceeding 100 μm. Microrods with smaller sizes of about several hundred nanometers were also observed. Fig. 1(b) shows the detailed morphology of a single ZnO microrod with a side length of ∼2 μm. The enlarged SEM image of the microrod exhibits a perfect hexagonal cross section and smooth surfaces, which benefit the formation of natural WGM microcavities and make such microrods ideal carriers for the study of CQDs/microcavity composites. A three-dimensional (3D) scheme of the WGM microcavity of the CQDs/ZnO microrod composite is shown in Fig. 1(c). The composite method is very simple. The CdSe/Zn_xCd_1−xS core/shell semiconductor CQDs solution were dropped on the ZnO microrod. After the solvent evaporation, it then formed a thin film of CQDs. Fig. 1(d) shows the HRTEM image of the CQDs/ZnO microrod composite. It can be clearly seen that a layer of CQDs closely covering the surface of the ZnO microrod. The interface between ZnO surface and CQDs layer was labelled with a red dotted line. The CQDs are well dispersed with a diameter of about 5 nm as marked out by red circles. Meanwhile, the well-resolved lattice fringes demonstrate the highly crystallined nature of the CQDs nanocrystals. Moreover, the EDS elemental mapping further identified the presence of ZnO in the core part and of CdSe/Zn_xCd_1−xS CQDs on the surface (Fig. 1(f–j)).Open in a separate windowFig. 1Typical SEM images of as-synthesized ZnO microrods: (a) low-magnification SEM image; (b) high-magnification SEM image revealing the morphology of an individual ZnO microrod with a hexagonal cross-section; (c) 3D scheme of a single core/shell CQDs and a CQDs/ZnO microrod composite; (d) HRTEM images of the above composite; (e) SEM image of a typical CQDs/ZnO composite; (f–j) EDS elemental mappings of O, Zn, Cd, Se, and S, respectively.The optical properties of the individual ZnO microrod were investigated by confocal micro-photoluminescence spectrometry using an excitation laser focused by a 40× objective to a ∼2 μm spot. PL spectra were recorded using a silicon charge-coupled-device (CCD) detector and a 600 line/mm grating. Photoluminescence imaging was carried out using a self-built confocal micro-photoluminescence spectrometer with a 405 nm laser. Fig. 2(a) shows atypical PL spectrum of the ZnO microrod, revealing the presence of a characteristic ZnO exciton emission in the UV range (around 380 nm) and abroad point defect emission band between 450 and 700 nm with clear modulations. The intensity of defect emission was stronger than that of exciton emission, and the absence of obvious emission resonant modes in the UV emission band were ascribed to a mode spacing too small to be resolved in the narrow UV band, with the optical absorption around the band edge region being larger. Fig. 2(b) depicts an expanded view of resonance peaks between 480 and 590 nm, clearly showing the microrod resonator for both TE (electrical component of light E⊥c-axis) and TM (E∥c-axis) polarization configurations. From the viewpoint of geometrical optics, two kinds of resonant cavity modes may form in the microrod cavity, namely simple WGM microcavities formed by multiple TIR from the six surfaces and F–P modes formed for two pairs of opposite facets. To determine the exact mode responsible for the signal, two adjacent peaks (λ₁ = 519.2 nm, λ₂ = 525.9 nm) of the TM signal were selected to calculate the path length (L) as follows:1where n is the refractive index of the medium, and dn/dλ is the dispersion relation, with Δλ (mode spacing between two adjacent peaks, also called free spectral range, FSR³⁴) = 6.7 nm, n = 2.06 (λ₁ = 519.2 nm), and λdn/dλ = −0.6 obtained using the refractive dispersion of ZnO in ref. 32. The calculated path length equaled ∼15.06 μm, and the side length (R) of the microrod used for the PL measurement equaled 2.94 μm, as determined by SEM imaging. If the resonant modes were simple F–P modes, the deduced values of L would equal 4R, i.e., ∼11.8 μm. Obviously, the calculated effective path length was much smaller than that (15.06 μm) calculated using eqn (1), which proved the above hypothesis wrong. Conversely, for the whispering gallery mode, the relevant path length was calculated as , agreeing with the theoretically calculated value given above. Thus, it was concluded that the observed resonant modes were mainly caused by the effect of the WGM microcavity. For the whispering gallery mode, the incident angle equaled 60°, with one full path featuring six TIRs. Such WGM microcavities can effectively control light emitted from ZnO itself, facilitating the research of light–matter interaction and the development of relevant optical devices.Open in a separate windowFig. 2(a) PL spectrum of an individual ZnO microrod. (b) Enlarged region of the above spectrum from 480 to 590 nm. (c) Corresponding ZnO dispersion relations. (d) Full-range PL spectra of ZnO (blue line), CQDs (blackline) and CQDs/ZnO (red line), respectively; inset shows a fluorescent image of the CQDs/ZnO composite. (e) The PL spectrum of CQDs in the range of 600–725 nm. (f) Corresponding resonator mode numbers of pure ZnO and the CQDs/ZnO composite in the range of 508–536 nm.To further explore the characteristics of the ZnO microrod WGM resonator, we identified the interference order N for TE and TM modes using the following equation:2where n is the refractive index of the ZnO sample, and N is the interference order of the resonant mode. The factor β is dependent on polarization. For TE polarization β = n, for TM polarization β = 1/n.The interference order N of the TE and TM modes were initially identified, using the refractive dispersion of ZnO microtubes.²⁶ The best fit of the interference order (N_TE = 47–66, N_TM = 48–67) was obtained by varying N systematically and the cavity length L within the experimental error. A similar fitting process has been utilized to calculate the refractive indices of ZnO microtubes.³⁵ These two series of integers are the interference orders for the relevant resonant modes between 480 nm and 590 nm. Using the obtained interference orders and the cavity length L, the accurate wavelength–dependent refractive dispersions (n_TE & n_TM) of the ZnO microrod were calculated. The dispersion relation is shown in Fig. 2(c), and the fitting Cauchy dispersion formula as follows:34It is worth noting that at a given wavelength, n_TM is larger than n_TE, with both indices decreasing with increasing wavelength.The formation of a CQDs/ZnO microrod WGM microcavity composite was confirmed by fluorescence imaging, which revealed that the ZnO microrod cavity was decorated with CQDs emitting red light with a wavelength of ∼650 nm (inset in Fig. 2(d)). To further elucidate the optical performance of the composite, we compared it with the PL spectrum of the pure CQDs and ZnO together. Interestingly, we found that some resonant peaks appear in the CQDs emission region in the CQDs/ZnO composite system. This indicates that the light of CQDs may be introduced into the ZnO microcavity and then was modulated. In fact, the thickness of the combined CQDs layer on the surface of the microcavity is critical for the optical resonance of the CQDs. If the combined CQDs layer was too thick, it will weaken the modulated light coupled in the microcavity emitted out. This phenomenon was also observed in other composite system.²⁸ In addition, it is worth noting that the CQDs emission was clearly blue-shifted after hybridization with the microcavity (Fig. 2(e)), probably due the formation of an oxidized layer on the CQDs surface under ambient conditions,²⁸ which also decreased the effective CQDs size. Fig. 2(f) shows an expanded view of resonance peaks between 508 and 536 nm, demonstrating that the resonant modes of the CQDs/ZnO microrod cavity were preferentially TM-polarized and clearly red-shifted, with TE modes being very weak and difficult to observe. This behavior was ascribed to the refractive index change of the medium caused by CQDs hybridization, as described by the following formula:³⁶5where n_CdSe is the refractive index of CQDs. The refractive index³⁷ of CQDs is n_CdSe = 1.73, which is larger than that of the air medium. For the same resonant peak, the wavelength of the resonant peak will increase with the decrease of the relative difference of the refractive index, resulting in a redshift as shown in Fig. 2(f). Moreover, the deposition of a CQDs layer on the surface of the microrod cavity mainly increases the optical loss of the TE polarization mode, complicating its detection.Interestingly, we also noticed that a broad and weak emission in the CQDs/ZnO composite microcavity appears obviously from 400 to 440 nm as shown in Fig. 3(a). And, the intensity of the exciton emission (from 370 to 390 nm) of ZnO decreases. In addition, we found that the CQDs used in our experiments also have a broad and weak emission at the same wavelength band as shown in Fig. 3(b). Moreover, the shape of the emission peak is very similar to that of the composite microcavity at the same region. This indicates there may be energy transfer between the ZnO and the combined CQDs. In fact, the broad weak emission was attributed to CdS CQDs, which synthesized along with the synthesis process of the core/shell CdSe/Zn_xCd_1−xS CQDs. From Fig. 3(c), it is clearly seen that the absorption spectrum of CdS CQDs covers the emission wavelength of the ZnO excitons at ∼390 nm. The central emission wavelength of CdS CQDs is ∼406 nm, and full width at half-maximum is 25 nm. After the CQDs attached to the surface of ZnO microrod, the distance between CQDs and microrod is close enough for fluorescence resonance energy transfer (FRET) to occur. The inset of Fig. 3(c) is the energy band structure of ZnO and CdS CQDs.^2,38 During FRET, the exciton of ZnO, initially in its electronic excited state, transfers its energy to the acceptor CdS via non-radiative dipole–dipole coupling, damping the band gap emission of the ZnO microrod and enhancing the emission intensity of CdS CQDs, which explains the PL spectra shown in Fig. 3(a). However, the above behavior was not observed when a purified CQDs solution (free of CdS CQDs) was used under the same experimental conditions (Fig. 3(d)), further verifying the occurrence of FRET in the CQDs/ZnO composite microcavity.Open in a separate windowFig. 3(a) PL spectra expanded in the range of 360–470 nm. (b) PL spectrum of CQDs in the range of 360–450 nm. (c) Absorption and PL spectra of CdS CQDs, with inset showing a FRET diagram with typical timescales. (d) PL spectra of CdS CQDs–free CdSe/Zn_xCd_1−xS core/shell CQDs, ZnO microrods, and the CQDs/ZnO composite.To clarify the nature of the resonance modes observed in the PL measurements, FEM simulations are used to study such ZnO or CQDs/ZnO microrod composite microcavity with hexagonal cross-section. Because of the two-dimensional (2D) nature of the measured optical modes, we only simulate a 2D model to simplify our calculation. In our simulations, the modeled microcavity with the same hexagonal cross-section as the fabricated microrod shown in Fig. 1(a) (i.e., a side length of 2.94 μm) is placed inside a simulation box surrounded by the well-matched layer boundaries to absorb the scattered electromagnetic fields. Here, TM polarization was chosen for comparing experimental and simulated results, and the dispersive refraction index of ZnO was therefore calculated from the PL spectrum of this material using eqn (3). The refractive index of CQDs was assumed to equal 1.73. And the dispersive refractive index of ZnO described by eqn (3) is directly imported into the software. The background medium in the simulation box was set to air or CdSe for investigating the microcavities of ZnO or the CQDs/ZnO composite, respectively. An electric current source was placed inside the 2D microcavity to excite TM-polarized optical modes. We choose a very dense mesh inside the ZnO microrod (<λ/20) and surrounding air (<λ/10) to guarantee the convergence of our results.The calculated radiation intensity spectra of the current source inside ZnO and CQDs/ZnO composite microcavities are shown in Fig. 4(b and d), respectively, revealing that if the radiation wavelength of the line source matches that of a microcavity resonance mode, its radiation is significantly enhanced, with these peaks being unambiguous signatures of the optical modes excited in the microcavity. In our calculation, the intensity of the current source was identical for all excitation wavelengths and, therefore, key information was provided only by the position of radiation peaks, with its intensity being negligible. For both ZnO and CQDs/ZnO composite microcavities, the resonance peaks of FEM-simulated radiation spectra well matched those observed experimentally (Fig. 4(a–d)), with the slight mismatch observed for CQDs/ZnO at short wavelengths attributed to the slight poor dispersion of CdSe that was ignored in our simulation (Fig. 4(c and d)). If the microcavity is surrounded by CQDs instead of the air, the resonance modes leak out of the ZnO microcavity more easily owing to the increased refraction index of the background medium, which increases the effective optical path for the resonance modes and induces their red shift (Fig. 4(b and d)). To justify these arguments, we further utilized the eigenmode analysis solver of COMSOL Multiphysics to search all eigen resonance modes supported by the two microcavities. For example, Fig. 4(e–h) show the electric field patterns of two representative resonance modes, clearly identifying the features of WGMs with N = 47 and 55. Likewise, the calculated resonance wavelengths (see insets) perfectly matched the peak positions marked by dashed lines in Fig. 4(a–d), demonstrating that N = 55 (N = 47) resonance modes shift from 547.8 nm (618.0 nm) in the ZnO microcavity to 556.9 nm (631.5 nm) in the CQDs/ZnO composite microcavity. In particular, the long-wavelength modes located in the fluorescence region of CdSe can indeed modulate the light emission of CQDs.Open in a separate windowFig. 4Measured PL spectra (a, c) and FEM-simulated radiation spectra (b, d) of a single ZnO microrod (a, b) and a CQDs/ZnO composite (c, d) with a hexagonal cross-section, and the corresponding WGM electric field distributions (e–h) at specified wavelengths.     

Reduced graphene oxide-mediated synthesis of Mn3O4 nanomaterials for an asymmetric supercapacitor cell

Herein, Mn₃O₄/reduced graphene oxide composites are prepared via a facile solution-phase method for supercapacitor application. Transmission electron microscopy results reveal the uniform distribution of Mn₃O₄ nanoparticles on graphene layers. The morphology of the Mn₃O₄ nanomaterial is changed by introducing the reduced graphene oxide during the preparation process. An asymmetric supercapacitor cell based on the Mn₃O₄/reduced graphene oxide composite with the weight ratio of 1 : 1 exhibits relatively superior charge storage properties with higher specific capacitance and larger energy density compared with those of pure reduced graphene oxide or Mn₃O₄. More importantly, the long-term stability of the composite with more than 90.3% capacitance retention after 10 000 cycles can ensure that the product is widely applied in energy storage devices.

The existence presence of rGO can affect the morphology of an Mn₃O₄/rGO composite, and the asymmetric supercapacitor cell created with this composite exhibits good capacitive performance.     

Ag3PO4 nanocrystals and g-C3N4 quantum dots decorated Ag2WO4 nanorods: ternary nanoheterostructures for photocatalytic degradation of organic contaminants in water

Visible-light-driven Ag₃PO₄/graphite-like carbon nitride/Ag₂WO₄ photocatalysts with different weight fractions of Ag₃PO₄ were synthesized. Ag₂WO₄ nanorods with a scale of 500 nm to 3 μm were prepared by using a hydrothermal reaction. Via a facile deposition–precipitation technique, graphite-like carbon nitride (g-C₃N₄) quantum dots and Ag₃PO₄ nanocrystals were then deposited onto the surface of Ag₂WO₄ nanorods sequentially. Under visible-light irradiation (λ > 420 nm), the Ag₃PO₄/g-C₃N₄/Ag₂WO₄ nanorods degraded Rh B efficiently and displayed much higher photocatalytic activity than that of pure Ag₂WO₄ and the g-C₃N₄/Ag₂WO₄ composite, and the Ag₃PO₄/g-C₃N₄/Ag₂WO₄ hybrid photocatalyst with 30 wt% of Ag₃PO₄ exhibited the highest photocatalytic activity. The quenching effects of different scavengers demonstrated that reactive h⁺ and ·O²⁻ played the major roles in Rh B degradation. It was elucidated that the excellent photocatalytic activity of Ag₃PO₄/g-C₃N₄/Ag₂WO₄ for the degradation of Rh B under visible light (λ > 420 nm) can be ascribed to the efficient separation of photogenerated electrons and holes through the Ag₃PO₄/g-C₃N₄/Ag₂WO₄ heterostructure.

The ternary heterostructured Ag₃PO₄/g-C₃N₄/Ag₂WO₄ photocatalysts were successfully synthesized. The ternary composites exhibited enhanced photocatalytic activity.     

Facile one-step hydrothermal synthesis of α-Fe2O3/g-C3N4 composites for the synergistic adsorption and photodegradation of dyes

With the expansion of industrialization, dye pollution has become a significant hazard to humans and aquatic ecosystems. In this study, α-Fe₂O₃/g-C₃N₄-R (where R is the relative percentage of α-Fe₂O₃) composites were fabricated by a one-step method. The as-prepared α-Fe₂O₃/g-C₃N₄-0.5 composites showed excellent adsorption capacities for methyl orange (MO, 69.91 mg g⁻¹) and methylene blue (MB, 29.46 mg g⁻¹), surpassing those of g-C₃N₄ and many other materials. Moreover, the ionic strength and initial pH influenced the adsorption process. Relatively, the adsorption isotherms best fitted the Freundlich model, and the pseudo-second-order kinetic model could accurately describe the kinetics for the adsorption of MO and MB by α-Fe₂O₃/g-C₃N₄-0.5. Electrostatic interaction and π–π electron donor–acceptor interaction were the major mechanisms for MO/MB adsorption. In addition, the photocatalytic experiment results showed that more than 79% of the added MO/MB was removed within 150 min. The experimental results of free-radical capture revealed that holes (h⁺) were the major reaction species for the photodegradation of MO, whereas MB was reduced by the synergistic effect of hydroxyl radicals (·OH) and holes (h⁺). This study suggests that the α-Fe₂O₃/g-C₃N₄ composites have an application potential for the removal of dyes from wastewater.

Simple one-step hydrothermal synthesis of α-Fe₂O₃/g-C₃N₄ composites for the synergistic adsorption and photodegradation of dyes     

Visible-light-responsive reduced graphene oxide/g-C3N4/TiO2 composite nanocoating for photoelectric stimulation of neuronal and osteoblastic differentiation

Restoration of nerve supply in newly formed bone is critical for bone defect repair. However, nerve regeneration is often overlooked when designing bone repair biomaterials. In this study, employing graphitic carbon nitride (g-C₃N₄) as a visible-light-driven photocatalyst and reduced graphene oxide (rGO) as a conductive interface, an rGO/g-C₃N₄/TiO₂ (rGO/CN/TO) ternary nanocoating with photoelectric conversion ability was fabricated on a Ti-based orthopedic implant for photoelectric stimulation of both bone and nerve repair. Compared with g-C₃N₄/TiO₂ (CN/TO) and TiO₂ nanocoatings, the ternary nanocoating exhibited stronger visible-light absorption as well as higher transient photocurrent density and open circuit potential under blue LED exposure. The improved photo-electrochemical properties of the ternary nanocoating were attributed to the enhanced separation of photogenerated carriers at the heterointerface. For the tested nanocoatings, introducing blue LED light irradiation enhanced MC3T3-E1 osteoblastic differentiation and neurite outgrowth of PC12 cells. Among them, the rGO/CN/TO nanocoating exerted the greatest enhancement. In a coculture system, PC12 cells on the ternary nanocoating released a higher amount of neurotransmitter calcitonin gene-related peptide (CGRP) under light irradiation, which in turn significantly enhanced osteoblastic differentiation. The results may provide a prospective approach for targeting nerve regeneration to stimulate osteogenesis when designing bone repair biomaterials.

rGO/g-C₃N₄/TiO₂ nanocoating was fabricated on Ti-based implant for photoelectric stimulation of bone and nerve repair. The ternary nanocoating exerted greater photoelectric effects on enhancing osteoblastic differentiation and neurite outgrowth.     

Electron-assisted synthesis of g-C3N4/MoS2 composite with dual defects for enhanced visible-light-driven photocatalysis

g-C₃N₄/MoS₂ composites were successfully prepared by an electron-assisted strategy in one step. Dielectric barrier discharge (DBD) plasma as an electron source, which has low bulk temperature and high electron energy, can etch and modify the surface of g-C₃N₄/MoS₂. The abundant N and S vacancies were introduced in the composites by plasma. The dual defects promoted the recombination and formation of heterojunctions of the g-C₃N₄/MoS₂ composite. It exhibited stronger light harvesting ability and higher charge separation efficiency than that of pure g-C₃N₄ and MoS₂. Compared with the sample by traditional calcination method, the plasma-sample showed better performance for degrading rhodamine B (RhB) and methyl orange. RhB is completely degraded within 2 hours on g-C₃N₄/MoS₂ by plasma. A mechanism for the photocatalytic degradation of organic pollutants via the composites was proposed. An electron-assisted strategy provides a green and effective platform to achieve catalysts with improved performance.

A N and S vacancies enriched g-C₃N₄/MoS₂ composite was prepared by plasma that promoted the formation of heterojunctions of the composite.     

Facile synthesis of porous Fe3O4@C core/shell nanorod/graphene for improving microwave absorption properties

Porous Fe₃O₄@C core/shell nanorods decorated with reduced graphene oxide (RGO) were fabricated through a facile one-pot method. The microwave absorption properties of the samples can be adjusted by the weight ratio of RGO. The addition of RGO not only effectively reduces the agglomeration of Fe₃O₄@C, but also has a great effect on impedance matching and dielectric loss, resulting in enhanced microwave absorption abilities. The thickness corresponding to optimum reflection loss (R_L) decreases as the weight ratio of RGO increases. For the Fe₃O₄@C/RGO composite, a maximum R_L value of −48.6 dB can be obtained at 13.9 GHz with a thickness of 3.0 mm, and the absorption bandwidth with R_L below −10 dB is 7.1 GHz from 10.9 GHz to 18 GHz. These results demonstrate a facile method to prepare a highly efficient microwave absorption material with special microstructure.

Porous Fe₃O₄@C core/shell nanorods decorated with reduced graphene oxide were synthesized by a facile one-pot method, and exhibit high microwave absorption performance: maximum reflection loss reaches −48.6 dB.     

The controlled synthesis of g-C3N4/Cd-doped ZnO nanocomposites as potential photocatalysts for the disinfection and degradation of organic pollutants under visible light irradiation

The in situ growth of well-dispersed Cd-doped ZnO nanoparticles (Cd-ZnO NPs) on graphitic carbon nitride (g-C₃N₄) nanosheets was successfully achieved through the co-precipitation method for the formation of Cd-doped ZnO nanocomposites with g-C₃N₄ (Cd-ZnO/g-C₃N₄ NCs). The effect of different compositions of ternary nanocomposites (Cd-ZnO/g-C₃N₄ NCs) on photocatalytic properties was investigated. Ternary NCs, in which 60% g-C₃N₄ hybridized with 7% Cd-doped ZnO (g-C₃N₄/Cd-ZnO) NCs were proven to be optimum visible-light-driven (VLD) photocatalysts for the degradation of methylene blue (MB) dye. The enhanced photodegradation of MB is mainly due to the increase in the generation of photogenerated charge carriers (reactive oxygen species (ROS), O²⁻, and ˙OH radicals). The electron spin resonance (ESR) experiment revealed that the superoxide and hydroxyl radicals were the leading species responsible for the degradation of MB. Moreover, the NC exhibited tremendous stability with a consistently high MB degradation rate for 10 successive catalytic cycles. The structural and optical properties of CdO, ZnO NPs, Cd-ZnO NPs, g-C₃N₄ NSs, and g-C₃N₄/Cd-ZnO NCs were investigated via XRD, SEM, EDX, TEM, FTIR spectroscopy, UV-Vis spectroscopy, ESR spectroscopy, and PL spectroscopy techniques. The synthesized photocatalysts were also applied against Gram-positive and Gram-negative bacterial strains to evaluate their antibacterial activities.

The controlled design of novel Z-scheme g-C₃N₄/Cd-ZnO heterojunction via chemical co-precipitation technique. 60% g-C₃N₄ hybridized with 7% Cd-doped ZnO (g-C₃N₄/Cd-ZnO) NCs have been proved to be optimum visible-light-driven (VLD) photocatalysts.     

Metal-free porous phosphorus-doped g-C3N4 photocatalyst achieving efficient synthesis of benzoin

Photocatalytic organic synthesis is mostly limited by the shortcomings of insufficient light absorption, high photogenerated electron–hole recombination rate and inadequate reactive sites of photocatalysts. To solve these problems, phosphorus-doped g-C₃N₄ with a porous structure was constructed. Benefiting from enhanced light absorption and electron–hole separation efficiency, PCNT has intensive oxygen activation ability to generate superoxide radicals, and is highly active in organic synthesis. In addition, PCNT has enhanced surface nucleophilicity, which is conducive to the carbon–carbon coupling process of the intermediate product benzaldehyde molecules and benzyl alcohol molecules in the benzoin condensation reaction. Metal-free PCNT is expected to replace the previously used highly toxic cyanide catalysts and provide a new way for the low-cost and efficient photocatalytic synthesis of benzoin.

Porous phosphorus-doped g-C₃N₄ (PCNT) has intensive oxygen activation ability to generate superoxide radicals, and can efficiently catalyze synthesis of benzoin from benzyl alcohol, with conversion rate and selectivity near to 100%.