The synthesis of graphene-TiO<Subscript>2</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> super-thin heterojunctions with enhanced visible-light photocatalytic activities

In this paper, an efficient strategy for the synthesis of graphene nanobelt-titanium dioxide/graphitic carbon nitride (graphene-TiO₂/g-C₃N₄) heterostructure photocatalyst was applied to fabricate a kind of visible-light-driven photocatalyst. The heterostructure shows higher absorption edge towards harvesting more solar energy compared with pure TiO₂ and pure g-C₃N₄ respectively. Furthermore, the as-prepared graphene-TiO₂/g-C₃N₄ heterostructure can show enhanced photocatalytic activity under visible-light irradiation. These outstanding performances of photocatalytic activities for graphene-TiO₂/g-C₃N₄ composites can be attributed to the heterojunction interfaces which can separate the electron-hole pairs and impede the recombination of electrons and holes more efficiently. This study conclusively demonstrates a facile and environmentally friendly new strategy to design highly efficient graphene-TiO₂/g-C₃N₄ heterostructure photocatalytic materials for potential applications under visible-light irradiation.

Open image in new window

Graphical abstract ?

     

Hierarchical structured ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>@RGO@TiO<Subscript>2</Subscript> composite as powerful visible light catalyst for degradation of fulvic acid

Hierarchical structured ZnFe₂O₄@reduced graphite oxide@TiO₂ (ZnFe₂O₄@RGO@TiO₂) nanocomposite was prepared by an electrostatic layer-by-layer route, which played a synthetic effect of Fenton oxidation of ZnFe₂O₄ and photocatalytic oxidation of TiO₂ to degrade fulvic acid (FA) solution under visible-light irradiation. In this method, RGO, as the middle layer, can effectively promote the photo-induced electron flow between the ZnFe₂O₄ and TiO₂ and further improve the efficiency of the photo-Fenton oxidation. The influencing factors on photo-Fenton oxidation, including solution pH, catalyst, and H₂O₂ dosage, have also been investigated. The results illustrated that the ternary composite presented the enhanced catalytic performance. Under visible light irradiation, the degradation efficiency of the sample on the FA solution can reach 95.4% within 3 h. In addition, the catalyst exhibited superior stability and reusability, and its degradation efficiency was still up to 90% after 5 cycles. Therefore, the composite will be a kind of efficient photocatalyst and had a promising application for visible-light driven destruction of organic pollutants.     

g-C3N4/SnS2异质结构:一类有潜力的光解水催化剂

采用第一性原理方法研究了层间耦合作用对g-C₃N₄/SnS₂异质结构的电子结构和吸光性质的影响.发现g-C₃N₄/SnS₂是一类典型的范德瓦异质结构,能有效吸收可见光,其价带顶和导带底与水的氧化还原势匹配,且由于电荷转移而导致的界面处极化场有利于光生载流子的分离.这些理论研究结果表明g-C₃N₄/SnS₂异质结构是一类非常有潜力的光解水催化材料.     

Solid state synthesis of nonstoichiometric Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> composites as visible-light photocatalyst

Nonstoichiometric Bi₂WO₆ photocatalyst with the composition of Bi_2?+?x WO_6?+?1.5x (?0.25 ≤ x ≤ 1) wa synthesized by a facile solid state reaction method. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The Bi_2.5WO_6.75 photocatalyst showed excellent visible-light-driven photocatalytic performance; nearly 100 % of RhB (10 ppm, pH?=?3?~?4) was decomposed within 25 min, which demonstrated that nonstoichiometric semiconductors could be an efficient visible-light-driven photocatalyst.     

Magnetically separable Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@C/BiOBr heterojunction for the enhanced visible light-driven photocatalytic performance

In this study, the magnetically recyclable Fe₃O₄@C/BiOBr heterojunction with enhanced visible light-driven photocatalytic ability was obtained by two-step solvothermal method. The phase, morphology, and structure of the samples were investigated by XRD, FESEM, HRTEM, and XPS. The Fe₃O₄@C/BiOBr heterojunction was composed of Fe₃O₄@C sphere and BiOBr microsphere with diameters of 200 nm and 1000 nm, respectively. The photocatalytic performance of Fe₃O₄@C/BiOBr composite for RhB was examined under visible light irradiation. The photocatalytic activity of Fe₃O₄@C/BiOBr composite was much higher than that of pure BiOBr and Fe₃O₄@C. After 35 min of irradiation, 97% of RhB could be removed with the Fe₃O₄@C/BiOBr photocatalyst. Based on radical trapping experiments of active species, the mechanism of enhanced photocatalytic performance was proposed. In addition, the superparamagnetic property of the photocatalyst not only allows its easy recyclability by an external magnetic field but also maintains high photocatalytic activity after five cyclic experiments.

Open image in new window

Graphical abstract ?

     

Carbon@SnS<Subscript>2</Subscript> core-shell microspheres for lithium-ion battery anode materials

A novel unique C@SnS₂ core-shell structure composites consisting of well-dispersity carbon microspheres and ultrathin tin disulfide nanosheets were successfully synthesized for the first time through a simple solvothermal method. The thin SnS₂ nanosheets grew onto the carbon microspheres surfaces perpendicularly and formed the close-knit porous structure. When it was used as anode materials for lithium-ion batteries, the hybrid C@SnS₂ core-shell structure composites showed a remarkable electrochemical property than pure SnS₂ nanosheets. Typically, the hybrid composites with SnS₂ nanosheet shells and carbon microsphere’s core exhibited an excellent initial discharge capacity of 1611.6 mAh/g. Moreover, the hybrid composites exhibited capacities of 474.8–691.6 mAh/g at 100 mA/g over 50 battery cycles, while the pure SnS₂ could deliver capacities of 243–517.6 mAh/g in the tests. The results indicated that the improvement of lithium storage performance of the core-shell structure C@SnS₂ anode materials in terms of rate capability and cycling reversibility owing to the introduction of the smooth carbon microspheres and special designing of core-shell structure.     

Synergistic effect of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> and CeO<Subscript>2</Subscript> co-modified titanate nanosheet heterojunction on enhanced photocatalytic degradation

CeO₂ and Fe₂O₃ co-modified titanate nanosheet (Fe₂O₃/CeO₂@TNS) was prepared by one-pot hydrothermal method; the photocatalyst exhibited large surface area with CeO₂ and Fe₂O₃ particles well dispersed on the surface. The results of XRD, BET, and Raman proved that the CeO₂ and Fe₂O₃ introduced in the TNS influenced its structure evolution from 3D to 2D. The modification resulted in a shift of the absorption edge toward a longer wavelength and the band gap reduced to 2.87 eV. The three-component systems performed excellent photocatalytic activity and cycle stability on phenol and methyl blue (MB) solution under sunlight; nearly total phenol and MB were degraded in dozens of minutes. And the reaction rate constant (K) of Fe₂O₃/CeO₂@TNS on phenol degradation was 1.77, 3.25, 4.88, and 13-fold of Fe₂O₃@TNS, CeO₂@TNS, bare TNS, and P25, respectively. The enhanced photocatalytic activity could be ascribed to the efficient separation of photogenerated pairs through the formation of tandem n-n-n heterojunction among the three-component systems. This work will be useful for the design of other tandem n-n-n heterojunction photocatalytic systems for application in energy conversion and environmental remediation.

Open image in new window

Graphical abstract ?

     

Synergistic effect of efficient adsorption g-C3N4/ZnO composite for photocatalytic property

Novel g-C₃N₄/ZnO composite photocatalyst was synthesized from an oxygen-containing precursor by direct thermal decomposition urea in air without any other templates assistance. Different percentages of g-C₃N₄ were hybridized with ZnO via the monolayer-dispersed method. The prepared g-C₃N₄/ZnO composites were characterized by XRD, SEM, UV–vis diffuse reflectance spectra (DRS), FT-IR, TEM and XPS. The composites showed much higher efficiency for degradation of Rhodamine B (RhB) than ZnO under UV and visible light irradiation. Especially, the photocatalytic efficiency was the highest under UV light irradiation when the percentage of g-C₃N₄ was 6%. The improved photocatalytic activity may be due to synergistic effect of photon acquisition and direct contact between organic dyestuff and photocatalyst. Then, effective separation of photogenerated electron–hole pairs at the interface of g-C₃N₄ is an important factor for improvement of photocatalytic activity. This work indicates that g-C₃N₄ hybrid semiconductors photocatalyst is a promising material in pollutants degradation.     

First-principles study of nitrogen defect g-C3N4/WS2 heterojunction on photocatalytic activity

In this work, first-principles density functional theory simulations have been performed to investigate the influence of nitrogen (N) defect on the supercell structure, electronic structure and photocatalytic properties of g-C₃N₄/WS₂ heterojunctions. Analyses of calculated binding energies and the lattice mismatch ratios led us to confirm that N-deficient g-C₃N₄ and WS₂ were in parallel contact and form a stable heterojunction. Furthermore, the work functions, molecular dynamics simulations, charge density differences, band structures, DOS, electronic and optical properties and absorption spectra of different g-C₃N₄/WS₂ heterojunctions have been analyzed in detail. It is revealed that the compositing of N-deficient g-C₃N₄ with WS₂ improves the separation of photoinduced electron-hole pairs. N-defect enhances the visible light absorption of the heterojunction, due to the introduction of impurity energy levels. Moreover, the introduction of defect species further improves the photocatalytic performance of g-C₃N₄/WS₂ heterojunction in the visible region.     

Fabrication and characterization of visible light-driven In<Subscript>2.77</Subscript>S<Subscript>4</Subscript>/In(OH)<Subscript>3</Subscript> composite photocatalysts with excellent redox performance

The In_2.77S₄ microspheres had been firstly fabricated by using polyethylene glycol (PEG) as the morphological modifier and then used to hybridize with In(OH)₃ nanocubes by a simply depositional method. The structure, optical properties, morphology, chemical compositions, and charge carrier behaviors of the as-prepared In_2.77S₄/In(OH)₃ composites were characterized, respectively. The methyl orange, tetracycline, rhodamine B, and Cr(VI) dilute solution were selected to evaluate their photocatalytic activities. Experimental results showed that In(OH)₃ nanocubes could improve the photocatalytic activity and recyclability of the In_2.77S₄ microspheres under the visible light irradiation. With the usage of In(OH)₃ increased, the photocatalytic efficiency of the hybrids was firstly increased and then decreased. When the mass ratios of In_2.77S₄ to In(OH)₃ were 6:2, it reached the maximum of 100% in 15 min for methyl orange, obviously higher than 67.4% of In_2.77S₄ and 1.1% of In(OH)₃. Meanwhile, it could also oxidize 85.6% of tetracycline in 20 min, 97.8% of rhodamine B in 7.5 min, and reduce 92.9% of Cr(VI) in 30 min under the visible light irradiation. Moreover, it could still degrade 91.7% of methyl orange solution after 3 cycles, which was much higher than 40.7% of In_2.77S₄ microspheres. In addition, the possible mechanism of enhancing photocatalytic properties was proposed.     

g-C3N4 modified Bi2O3 composites with enhanced visible-light photocatalytic activity

Novel g-C₃N₄ modified Bi₂O₃ (g-C₃N₄/Bi₂O₃) composites were synthesized by a mixing-calcination method. The samples were characterized by thermogravimetry (TG), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS), photoluminescence (PL) and photocurrent-time measurement (PT). The photocatalytic activity of the composites was evaluated by degradation of Rhodamine B (RHB) and 4-chlorophenol (4-CP) under visible light irradiation (>400 nm). The results indicated that the g-C₃N₄/Bi₂O₃ composites showed higher photocatalytic activity than that of Bi₂O₃ and g-C₃N₄. The enhanced photocatalytic activity of the g-C₃N₄/Bi₂O₃ composites could be attributed to the suitable band positions between g-C₃N₄ and Bi₂O₃. This leads to a low recombination between the photogenerated electron–hole pairs. The proposed mechanism for the enhanced visible-light photocatalytic activity of g-C₃N₄/Bi₂O₃ composites was proven by PL and PT analysis.     

Growth of FePO<Subscript>4</Subscript> nanoparticles on graphene oxide sheets for synthesis of LiFePO<Subscript>4</Subscript>/graphene

FePO₄·xH₂O/graphene oxide (FePO₄·xH₂O/GO) composites were prepared by a facile chemical precipitation method. Using the as-prepared FePO₄·xH₂O/GO and LiOH·H₂O as precursors and followed by carbothermal reduction, LiFePO₄/graphene composites were obtained. Scanning electron microscope (SEM) images indicated that the graphene had very good dispersity and uniformly attached to the LiFePO₄ particles. The conductive framework of graphene improved the electrochemical properties of the composites. The composites deliver high initial discharge capacity of 163.4 mAh g^?1 as well as outstanding rate performance.     

Fabrication of In-rich AgInS<Subscript>2</Subscript> nanoplates and nanotubes by a facile low-temperature co-precipitation strategy and their excellent visible-light photocatalytic mineralization performance

Visible-light-driven In-rich AgInS₂ nanoplates and nanotubes were successfully prepared by a convenient co-precipitation strategy at low temperature. The effect of different In/Ag molar ratio in the raw materials on the physicochemical properties and photocatalytic activity of AgInS₂ was investigated. The In/Ag molar ratio has an obvious effect on the morphology of AgInS₂, and the physicochemical properties and photocatalytic activity of AgInS₂ are also dependent on the In/Ag molar ratio. When the molar ratio of In/Ag is 9, the photoluminescence intensity of AgInS₂ reaches a minimum value, while its photocurrent density is maximum (0.011 mA/cm²), indicating the most efficient separation of electron-hole pairs. The AgInS₂ with the In/Ag molar ratio of 9 exhibits the highest visible-light photocatalytic activities with almost complete degradation of 2-nitrophenol, which is attributed to the narrowest band gap and the most efficient separation of electron-hole pairs. Moreover, In-rich AgInS₂ exhibits excellent regeneration ability.     

石墨相氮化碳的制备条件优化用以提高其在可见光下的光催化活性

通过染料的光降解实验和敏感性数学分析探讨了石墨相氮化碳(g-C₃N₄)的制备条件与其稳定性和光催化活性之间的联系. 结果表明,相比于焙烧时间,焙烧温度的改变更为显著地影响了g-C₃N₄ 的光催化活性. 制备条件优化之后的g-C₃N₄在可见光照射下催化降解罗丹明B(RhB)的活性比未优化时提高了约100倍,归因于材料比表面积的增大和表面光生电子-空穴迁移速度的增强.     

One-dimensional Bi<Subscript>2</Subscript>Mo<Subscript>x</Subscript>W<Subscript>1-x</Subscript>O<Subscript>6</Subscript> sosoloids: controllable synthesis by electrospinning process and enhanced photocatalytic performance

One-dimensional Bi₂Mo_xW_1-xO₆ (x = 0, 0.2, 0.5, 0.67, and 1) photocatalysts have been successfully synthesized for the first time by a straightforward electrospinning technique with a calcination process. The as-formed Bi₂Mo_xW_1-xO₆ nanofibers are composed of inter-linked nanosheets of 30–50 nm in size and characterized by thermogravimetric and differential scanning calorimetric, Fourier transform infrared, Raman spectra, X-ray powder diffraction, scanning electron microscope, Brunauer-Emmett-Teller, transmission electron microscope, UV-Vis spectroscopy, photoluminescence, HPLC, and EIS. The photodegradation behaviors towards organic dyes, including rhodamine B (RhB) and methylene blue (MB) are investigated, and the results illustrate that Bi₂Mo_0.25W_0.75O₆ nanofibers exhibit the highest photocatalytic performance under visible light irradiation than Bi₂Mo_xW_1-xO₆ (x = 0, 0.2, 0.5, 0.67, and 1) samples. The possible mechanisms of the enhanced photocatalytic properties are discussed in detail.     

Semiconducting SnO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript> (S-T) composites for detection of SO<Subscript>2</Subscript> gas

SnO₂-TiO₂ (S-T) composites with different molar ratios were prepared by mechanical mixing followed by sintering at 700 °C for 4 h in air. The structural and microstructural properties of the composites were investigated using powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). S-T composites were investigated by introducing SO₂ to test their chemical stability using PXRD and SEM coupled with energy dispersive X-ray (EDX) analysis. The sensing performance was measured at different temperatures using various SO₂ concentrations (10–100 ppm). A composite comprising 25 mol% of SnO₂ and 75 mol% TiO₂ (S25-T75) exhibited the highest sensitivity comparing to other S-T composites studied under the presently investigated conditions. t ₉₀ (90 % of response time) was found to be ～5 min for thick pellet (~2 mm in thickness). SO₂ sensing mechanism has been explained through the band structure model.     

Characterization and optimization of Ce0.6Zr0.4−x Mn x O2 (x ≤ 0.4)

In situ synthesis method is used to synthesize g-C₃N₄-P25 composite photocatalysts with different mass rations. The experiment result shows that P25 particles with diameter at range of 20–30 nm were embedded homogenously in the sheets of g-C₃N₄. Coupling g-C₃N₄ with P25 can not only improve the visible light absorption, but also improve the visible light photocatalytic activity of P25. The g-C₃N₄-P25 nanocomposite has the higher photocatalytic activity than g-C₃N₄ under visible light. The optimal g-C₃N₄ content with the highest photocatalytic activity is determined to be 84 %, which is almost 3.3 times higher than that of individual g-C₃N₄ under the visible light. The enhanced visible light photocatalytic activity could be ascribed to the formation of g-C₃N₄ and TiO₂ heteojunction, which results in an efficient separation and transfer of photo-induced charge carriers. The electron spin resonance results show that the ^·O₂ ^? radicals are main active species for g-C₃N₄ and the g-C₃N₄-P25 nanocomposites.     

Synthesis and electrical conductivity of a new Ag<Subscript>6</Subscript>SnS<Subscript>4</Subscript>Br<Subscript>2</Subscript> superionic compound

The conditions of synthesizing a new Ag₆SnS₄Br₂ compound were studied. The crystallographic parameters of the unit cell were determined as follows: space group Pnma, a=6.67050(10) Å, b=7.82095(9) Å, c=23.1404(3) Å, and Z=4. The total electrical conductivity and its ionic component were measured by a dc probe method in the temperature range 210–380 K. Kinks in the conductivity curve and the differential thermogram of heating the alloy were revealed at 235 K. It was concluded that the mass and charge transfers in the compacted Ag₆SnS₄Br₂ alloy powder have an intragrain character.     

One-step synthesis of Ag<Subscript>2</Subscript>S/Ag@MoS<Subscript>2</Subscript> nanocomposites for SERS and photocatalytic applications

This paper reported a one-step synthesis of Ag₂S/Ag@MoS₂ nanocomposites and its applications in the surface-enhanced Raman scattering (SERS) detection and photocatalytic degradation of organic pollutants. The nanocomposites were well characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammograms (CV), the Brunauer-Emmett-Teller (BET), and Fourier transforms infrared spectra (FTIR). The AgNPs were uniformly dispersed on the MoS₂ nanosheets and the particle size of the AgNPs was about 10–30 nm. These Ag₂S/Ag@MoS₂ nanocomposites offered sensitive SERS signals for the detection of R6G with the limit of detections as low as 10^?10 M. The photocatalytic activity of the composite catalyst was studied by the degradation of methylene blue (MB) dye under light illumination. The apparent rate constant of MB degradation for the obtained catalyst could reach 6.6?×?10^?2 min^?1, indicating that the novel Ag₂S/Ag@MoS₂ nanocomposites can be explored for organic pollutant’s detection and degradation.

Open image in new window

Graphical abstract One-step synthesis of Ag₂S/Ag@MoS₂ nanocomposites for SERS and photocatalytic applications

     

Remarkable catalytic activity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript> nanocomposites prepared by hydrothermal method for the degradation of methyl orange

Visible light Bi₂O₃/TiO₂ nanocomposites are successfully prepared with different dosages of Bi₂O₃ by hydrothermal process. All the as-prepared samples are characterized by X-ray diffraction (XRD), scanning and transmission electron microscopes (SEM and TEM), Brunauer-Emmett-Teller analysis (BET), N₂ adsorption-desorption measurement, and UV-Vis diffuse reflectance spectra (DRS). XRD and Raman spectra reveal the anatase phase of both TiO₂ and Bi₂O₃/TiO₂ nanocomposites. X-ray diffraction patterns demonstrate that the bismuth ions did not enter into the lattice of TiO₂, and Bi₂O₃ is extremely dispersive on the surface of TiO₂ nanoparticles. The incorporation of Bi₂O₃ in TiO₂ leads to the spectral response of TiO₂ in the visible light region and efficient separation of charge carriers. The enhanced visible light activity is tested by the photocatalytic degradation of methyl orange under light illumination, and the performance of Bi₂O₃/TiO₂ nanocomposites are superior than that of pure TiO₂ which is ascribed to the efficient charge separation and transfer across the Bi₂O₃/TiO₂ junction. Bi₂O₃/TiO₂ nanocomposite (20 mg) loaded with 0.25 of Bi₂O₃ dispersed in 50 ml of 5 ppm methyl orange solution exhibited the highest photocatalytic activity of 98.86% within 240 min of irradiation, which is attributed to the low band gap, high surface area, and the strong interaction between Bi₂O₃ and TiO₂.