g-C3N4/g-C3N4 isotype heterojunction as an efficient platform for direct photodegradation of antibiotic

A visible-light-driven g-C₃N₄/g-C₃N₄ isotype heterojunction photocatalyst was synthesized by one-step thermal treatment using urea and thiourea as the precursor. The photocatalytic activity of as-prepared photocatalyst was evaluated through the degradation of rhodamine B (RhB) and tetracycline hydrochloride (TC) under the visible light irradiation. The hybrid showed enhanced photocatalytic activity in photodegradating the applied pollutants as compared with single g-C₃N₄. When the ratio of urea to thiourea was 2:1, the prepared isotype heterojunction exhibited the highest photocatalytic activity and the photodegradation rates for RhB and TC were 99.8% and 95.1% after being visible light irradiated for 1 h and 4 h respectively. The enhanced photocatalytic performance of the isotype heterojunction is ascribed to the enhanced charge separation efficiency. After being reused for 5 times, the hybrid still showed excellent recyclability and chemical stability. Furthermore, NaI, BQ and IPA were used as the sacrificial agents for studying the surface reactions in the photocatalytic process. The method used in this work provides a new pathway to achieve more efficient degradation of antibiotics and to stimulate further studies in this important field.     

Enhanced photocatalytic degradation of industrial dye by g-C3N4/TiO2 nanocomposite: Role of shape of TiO2

The photocatalytic degradation of toxic dyes has brought a new revolution to reduce water pollution. To degrade industrial dyes, TiO₂ is an important photocatalyst but the role of morphology is also important in degradation. We have synthesized g-C₃N₄/TiO₂ nanocomposite (1:1) having different shapes of TiO₂ (nanorods (NR), nanospheres (NS), and nanotubes (NT)), to show the effect of morphology on its photocatalytic activity. To improve the photocatalytic efficiency of TiO₂ in visible light, we have incorporated g-C₃N₄, a visible light active photocatalyst. The HRTEM, FESEM and Electron Diffraction studies with color mapping indicate successful synthesis of g-C₃N₄/TiO₂ nanocomposites. The increased photocatalytic efficiency of the nanocomposites regarding the degradation of Rhodamine B (RhB) dye under visible light irradiation is due to the incorporation of g-C₃N₄ with different shapes of TiO₂. The studies show that, the shape of TiO₂ has a remarkable effect in photodegradation. The best degradation performance (～97%) was obtained from g-C₃N₄/TiO₂ -nanotubes composite with a rate constant of 0.0403?min^?1 within 80?min, whereas degradation efficiency of other shapes of TiO₂ like NS (92%) and NR (94.5%) were also found to be greater than that of commercial TiO₂ (P25) composite (74%). Results from UV–Vis absorption study, X-ray Diffraction studies, X-ray photoelectron spectroscopy and BET analysis suggest that the improvement in photocatalytic activity of composite is due to increased light absorption in visible region and increase in surface area (137.1?m²/g). Results from different scavengers study (DMSO, ascorbic acid and methanol) indicate that electron and superoxide ions act as main reactive species in photodegradation of RhB dye. The reusability efficiency of the catalyst shows 86% degradation after 5 consecutive cycles. The effect of pH and catalyst concentration was also determined which shows that maximum degradation occurs at pH?～?7 (98%) and degradation efficiency is increased with increase of catalyst dose from 0.1?mg/ml to 0.6?mg/ml and after that saturation occur due to increase in opacity and scattering of light. A comparative study was done with literature which suggests that this nanocomposites act as one of the best photocatalysts for degradation of toxic dyes.     

Preparation of visible light responsive g-C3N4/H-TiO2 Z-scheme heterojunction with enhanced photocatalytic activity for RhB degradation

The development of high-efficiency heterojunction with improved photocatalytic property is regarded as a promising way to decontaminate wastewater. In this study, Z-Scheme g-C₃N₄/H-TiO₂ heterojunctions with different proportions were synthesized. The photocatalytic degradation of rhodamine B (RhB) was studied under visible light irradiation. Among them, 10% g-C₃N₄/H-TiO₂ photocatalyst had the best performance, and the degradation rate of RhB was 65% within 120 min. In addition, 10% g-C₃N₄/H-TiO₂ photocatalyst had high stability, and its photocatalytic activity did not decrease significantly after four cycles. Through photocurrent analysis, it is found that the photogenerated carriers have obviously excellent separation and transfer characteristics, which makes the 10% g-C₃N₄/H-TiO₂ photocatalyst have good degradation performance. Electron paramagnetic resonance (ESR) experiments showed that ·OH and ·O₂^? were active radicals during degradation.

     

Carbon dot sensitized integrative g-C3N4/AgCl Hybrids: An synergetic interaction for enhanced visible light driven photocatalytic process

Rational design of organic-inorganic heterojunction photocatalyst has become a research hotspot of recent researchers due to their abundance and cost effectivity. Herein, we present the integrated photocatalyst carbon dot (CD) decorated on g-C₃N₄/AgCl heterojunction synthesized by simple impregnation method. The primary confirmation for the as-prepared samples has been carried out by various characterization techniques. From the obtained results, the ternary nanocomposite demonstrated a prominent photocatalytic activity which was almost 10 and 51 fold higher than pure g-C₃N₄ in the degradation of organic dyes. The reasons behind the improved efficiency are (i) The introduced CD facilitates broader absorption in the visible region because of π-conjugated CDs and provide favorable electron kinetics by creating trap states at the CD/g-C₃N₄ interface. (ii) The AgCl acts as an electron sinker and reduce the carrier’s recombination. To justify the photocatalytic activity, a possible mechanism was proposed and verified by trapping experiments. Finally, this approach could be a new one in an organic-inorganic hybrid photocatalyst for the degradation of organic dyes.     

The pre-acidizing corrosion on the surface of TiO2 enhanced the photocatalytic activity of g-C3N4/TiO2

In this work, g-C₃N₄/TiO₂ nanocatalysts were prepared by high-voltage electrospinning and hydrothermal methods. The surface of the pure TiO₂ nanomaterial was treated by acidification before it was combined with g-C₃N₄.Various characterization methods were used to characterize the prepared photocatalyst. RhB (20 mg/L) was degraded as a target-degradable pollutant, the degradation efficiency of the nanocatalyst was measured under UV–Visible light. The results show that the degradation efficiency of the g-C₃N₄/TiO₂ nanocomposite material that has undergone pre-acidification treatment is much higher than that of the untreated catalyst.

     

Deposition of CuWO4 nanoparticles over g-C3N4/Fe3O4 nanocomposite: Novel magnetic photocatalysts with drastically enhanced performance under visible-light

Novel g-C₃N₄/Fe₃O₄/CuWO₄ nanocomposites, as magnetic visible-light-driven photocatalysts, fabricated through a simple refluxing-calcination process. The synthesized photocatalysts were characterized by a series of techniques including XRD, EDX, SEM, TEM, HRTEM, FT-IR, TGA, BET, UV–vis DRS, PL, and VSM. The results showed that heterojunctions are formed between g-C₃N₄, Fe₃O₄, and CuWO₄, which favor suppression of the photogenerated electron/hole pairs from recombination. The resultant g-C₃N₄/Fe₃O₄/CuWO₄ (30%) sample exhibited superior photocatalytic performance. The degradation rate constants on the g-C₃N₄/Fe₃O₄/CuWO₄ (30%) nanocomposite were almost 10.5, 17, 12.5, and 42.5 times higher than those of the pristine g-C₃N₄ for degradations of RhB, MB, MO, and fuchsine, respectively. Moreover, the photocatalyst was magnetically separated and recycled with negligible loss in the activity, which is important for the sustainable photocatalytic processes. Thus, the ternary nanocomposite could have potential applications in different photocatalytic processes.     

Novel ternary g-C3N4/Fe3O4/MnWO4 nanocomposites: Synthesis,characterization, and visible-light photocatalytic performance for environmental purposes

The g-C₃N₄/Fe₃O₄/MnWO₄ nanocomposites were prepared by a refluxing-calcination procedure. Visible-light-induced photocatalytic experiments showed that the g-C₃N₄/Fe₃O₄/MnWO₄ (10%) nanocomposite has excellent ability to degrade a range of contaminants including rhodamine B, methylene blue, methyl orange, and fuchsine, which is about 7, 10, 25, and 31 times of the g-C₃N₄ photocatalyst, respectively. Reactive species trapping experiments revealed that superoxide anion radicals play major role in the photodegradation reaction of rhodamine B (RhB). After the treatment process, the utilized photocatalyst was magnetically recovered and reused with negligible loss in the photocatalytic activity, which is vital in the photocatalytic processes. Finally, a mechanism was proposed for the enhanced interfacial carrier separation and transfer and the improved photocatalytic performance.     

Enhancement of photocatalysis performance of CdIn2S4/g-C3N4 heterojunction by H2O2 synergism

A highly efficient binary CdIn₂S₄/g-C₃N₄ heterojunction photocatalyst was synthesized by a simple wet impregnation method. Photocatalytic system based on the synergistic action of binary CdIn₂S₄/g-C₃N₄ heterojunction and H₂O₂ was proposed to improve the degradation effect of dyes. The photocatalytic activity was evaluated by the degradation of methyl orange(MO) under visible light irradiation. The results demonstrated that contrasted to pure g-C₃N₄, the synthesized heterojunction can significantly improve the photocatalytic activity. After 120 min of irradiation by visible light, the photocatalytic efficiency of MO degradation of 7CIS/CN was 3.13 times higher than that of g-C₃N₄. When 60 mM H₂O₂ was added on this basis, the photocatalytic efficiency increased from 93.81 to 99.40%. The improvement of photocatalytic activity is attributed to the formation of binary CdIn₂S₄/g-C₃N₄ heterojunction to promote the transfer of photogenerated electron-hole pairs, and an appropriate amount of H₂O₂ as an electron trap further reduced the recombination rate of photogenerated electron-hole pairs. Active species capture experiments showed that ·O₂^? are the main active substances. Subsequently, the mechanism of photocatalytic degradation was proposed. This work provided a new efficient strategy for the degradation of industrial dye wastewater.

     

Fly ash cenospheres as multifunctional supports of g-C3N4/N-TiO2 with enhanced visible-light photocatalytic activity and adsorption

The ternary composites of g-C₃N₄/N-TiO₂/FACs (FAC: Fly Ash Cenospheres) were synthesized by an in-situ hydrolysis method to improve the photocatalytic activity and their stability. When TiO₂ was anchored on FAC, it was easily to be separated from the aqueous solution and could be repeatedly utilized. In the present experiments, the degradation rate remained for more than 68% even after the composite reused for seven times. The band gap of g-C₃N₄/N-TiO₂/FAC was 2.75?eV, which might be owing to the synergistic effect between N-TiO₂ and g-C₃N₄. The composite of g-C₃N₄/N-TiO₂/FAC had an ideal activity of 72.2% under visible light illumination for 180?min. It was about 1.3 times of N-TiO₂/FAC and 3.5 times of g-C₃N₄. The synergistic effect of SiO₂, Fe₂O₃ and TiO₂ components resulted to the improvement of photocatalytic performance.     

Synthesis of AgBr/TiO2/(I/S) composite and its enhanced photocatalytic performance to rhodamine B

Novel AgBr/TiO₂/(I/S) composite was synthesized by deposition–precipitation method. The AgBr/TiO₂/(I/S) composite was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, UV–Vis diffuse reflectance spectra and the N₂ adsorption/desorption instrument. Under visible light irradiation, AgBr/TiO₂/(I/S) composite displayed much higher photocatalytic activity than that of pure I/S in the degradation of Rhodamine B (RhB). The RhB dye was degraded by 89% in less than 100 min. All results indicated that AgBr/TiO₂/(I/S) composite have good photocatalytic activity and chemical stability. Moreover, ·O₂^? is demonstrated to be the dominant radical for the photocatalytic degradation of RhB.

     

ZnGaNO solid solution–C3N4 composite for improved visible light photocatalytic performance

ZnGaNO solid solution–C₃N₄ composite photocatalyst with visible light response was synthesized through polymerization of melamine in the presence of ZnGaNO solid solution. The composite photocatalyst was characterized by X-ray diffraction, high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FT-IR) spectroscopy, UV–vis diffuse reflection spectroscopy, X-ray photoelectron spectroscopy (XPS), Energy dispersed spectrometer (EDS) and BET surface area measurements. The activity of composite photocatalyst g-C₃N₄–ZnGaNO for photodegradation of methyl orange (MO) is higher than that of either single-phase g-C₃N₄ or ZnGaNO solid solution. The as-prepared composite photocatalyst exhibits an improved photocatalytic activity due to enhancement of electron–hole separations at the interface.     

Novel g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> wrapped γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> microspheres heterojunction for efficient photocatalytic application under visible light irradiation

The novel g-C₃N₄ wrapped γ-Al₂O₃ microspheres heterojunction was successfully prepared by a simple hydrothermal process followed by calcination. The photocatalytic performances of the composite were evaluated by the degradation of methyl orange (MO) and rhodamine B (RhB) under visible light irradiation. The obtained Al₂O₃/g-C₃N₄ heterojunction exhibited much higher photocatalytic activity compared to pure g-C₃N₄. The enhanced performance may be mainly attributed to the tight contact between the components of the heterostructure as well as the efficient transfer of photoinduced electrons from the valence band (VB) of g-C₃N₄ to the defect sites of γ-Al₂O₃. The trapping experiment results indicated that the ·O₂ ^? radicals and holes (h⁺) are main active species in the decomposition of MO. This work will provide new ideas for manipulation of high-performance heterojunction for practical photocatalysis applications in water pollution controls.     

N-TiO<Subscript>2</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/Up-conversion phosphor composites for the full-spectrum light-responsive deNO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> photocatalysis

The ternary composites consisted of nitrogen-doped titanium dioxide, carbon nitride and up-conversion phosphors (UP) were successfully prepared by a solvothermal method. The heterojunction could be formed when N-TiO₂ and g-C₃N₄ were combined together. The composite of N-TiO₂/g-C₃N₄@UP had excellent ultraviolet, visible and infrared light absorption, indicating the possibility for the utilization of full spectrum of solar light. When N-TiO₂ was coupled with g-C₃N₄ and up-conversion phosphors to form a composite, the visible light and NIR light absorption of the samples increased. The ternary composite N-TiO₂/g-C₃N₄@G-UP presented reasonable deNO _x performance of about 8.0% under the irradiation of IR light of 980 nm. The intensification of the photocatalysis might be realized by utilizing up-conversion phosphors, which could convert low-energy NIR light into high-energy photons (visible light) and increase the efficient irradiation on the surface of photocatalyst.     

Construction of interface electric field by electrostatic self-assembly: enhancing the photocatalytic performance of 2D/2D Bi12O17Cl2/g-C3N4 nanosheets

Bi₁₂O₁₇Cl₂ is an ideal photocatalytic material with an appropriate band gap and visible light absorption. However, the performance of a single Bi₁₂O₁₇Cl₂ photocatalytic material is still limited by the low separation rate of photogenerated electrons and holes. In this paper, the 2D Bi₁₂O₁₇Cl₂ and 2D g-C₃N₄ materials were prepared, and fabricated 2D/2D Bi₁₂O₁₇Cl₂/g-C₃N₄ nanosheets by electrostatic self-assembly using the different surface electrical properties of the two materials. The formation of an electric interface field between Bi₁₂O₁₇Cl₂ and g-C₃N₄ nanosheets and the matched energy band structure of the two materials can effectively promote the separation of electrons and holes and reduce recombination to improve the photocatalytic performance of semiconductor materials. The Bi₁₂O₁₇Cl₂/g-C₃N₄ with appropriate composite ratio has good degradation activity of Rhodamine-B (RhB) organic pollutants. The composite material can degrade nearly 100% of 10 ppm RhB in the reaction time of 2 h under neutral conditions and completely degrade rhodamine B in 90 min under acidic conditions.

     

In<Subscript>2</Subscript>S<Subscript>3</Subscript> nanoparticles dispersed on g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanosheets: role of heterojunctions in photoinduced charge transfer and photoelectrochemical and photocatalytic performance

Fast recombination of photogenerated charge carriers is a major problem in the photoelectrochemical and photocatalytic processes. In this work, we report significantly improved PEC performance of a nanocomposite consists of In₂S₃ nanoparticles dispersed on g-C₃N₄ nanosheets synthesized by a simple and facile wet chemical route. The results of high-resolution TEM study show that the obtained In₂S₃ nanoparticles of size 10–20 nm exist in cubic phase and are uniformly dispersed on the surface of g-C₃N₄ nanosheets. The In₂S₃/g-C₃N₄ nanocomposite with 25 weight percentage of In₂S₃ exhibits 8.5 times higher photocurrent density than the single-phase g-C₃N₄ under visible light illumination. The enhanced photocurrent density exhibited by the In₂S₃/g-C₃N₄ nanocomposite is attributed to the efficient separation of photogenerated charge carriers. The charge transfer mechanism in In₂S₃/g-C₃N₄ heterojunction was studied by a series of experiments, such as electrochemical impedance spectroscopy, photoelectrochemical measurement and photoluminescence emission spectroscopy. The intimate interface promotes the charge transfer and inhibits the recombination rate of photogenerated electron–hole pairs, which significantly improves the photoelectrochemical performance. A detailed charge transfer mechanism is discussed based on the Mott–Schottky plot study. This heterojunction material is found to be an efficient photocatalyst for the degradation of both cationic rhodamine B dye and anionic methyl orange dye as the lifetime of photogenerated charge carriers is higher in the composite than in single-phase In₂S₃ and g-C₃N₄. A strong correlation between the photoelectrochemical and the photocatalytic performances is observed in this composite.     

SnO2/g-C3N4 photocatalyst with enhanced visible-light photocatalytic activity

Visible light-responsive SnO₂/g-C₃N₄ nanocomposite photocatalysts were prepared by ultrasonic-assisting deposition method with melamine as a g-C₃N₄ precursor. The as-prepared photocatalysts were characterized by X-ray diffraction, transmission electron microscopy, UV–vis diffuse reflectance spectroscopy, Fourier transform infrared spectra and photoluminescence emission spectra. The photocatalytic activities of the samples were evaluated by monitoring the degradation of methyl orange solution under visible light irradiation (wavelength ≥400 nm). The results show that the SnO₂ nanoparticles with the size of 2–3 nm are dispersed on the surface of g-C₃N₄ evenly in SnO₂/g-C₃N₄ nanocomposites. The visible-light photocatalytic activity of SnO₂/g-C₃N₄ nanocomposites is much higher than that of pure g-C₃N₄, and increases at first and then decreases with the increment of the content of g-C₃N₄ in the nanocomposites. The visible-light photocatalytic mechanism of the investigated nanocomposites has been discussed.     

Highly enhanced photocatalytic degradation of dye rhodamine B on the biogenic hierarchical porous TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript> with 1D/3D-chain

A hybrid photocatalyst consisting of TiO₂ and nonporous SiO₂ (TiO₂/CS-RH) is prepared by loading TiO₂ sol on one-dimensional/three-dimensional chain (1D/3D-chain) which is synthesized from rice husk. The products are characterized by X-ray diffraction, N₂-adsorption–desorption analysis and scanning electron microscopy. Meanwhile, the corresponding photocatalytic activity is evaluated by measuring the photocatalytic oxidation of rhodamine B (RhB). The results reveal that TiO₂/CS-RH displays a hierarchical porous structure from micrometer to nanometer scale with high BET surface area (574.7–719.4 cm²/g). Meanwhile, the activity of TiO₂/CS-RH for the photocatalytic degradation of RhB in aqueous slurry is significantly higher than that of the unsupported TiO₂. The optimal TiO₂ loaded on the support was two times and then treated at 600 °C for 120 min to complete the conversion of RhB. In contrast, the unsupported TiO₂ photocatalyst could convert only 20% of RhB in the same irradiation time and condition.     

Efficient visible-light driven photocatalysts: coupling TiO<Subscript>2</Subscript>(AB) nanotubes with g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanoflakes

The wide application of the titanium dioxide (TiO₂) as the photocatalysts is greatly hindered by its intrinsic large band gap and usually fast electron–hole recombination. Here, we reported the exploration of coupling g-C₃N₄ nanoflakes to TiO₂ nanotubes with the anatase and TiO₂(B) mixed phases (TiO₂(AB)) toward the efficient visible-light-driven hybrid photocatalyst. It is found that coupling TiO₂(AB) nanotubes with g-C₃N₄ nanoflakes could bring a profoundly extension the visible light adsorption capacity and enhanced photogenerated carrier separation. Accordingly, they exhibit much higher efficient photocatalytic activities toward the degradation of sulforhodamine B under the visible light irradiation, which is enhanced for nearly 15 times to those of the TiO₂(AB) and g-C₃N₄, suggesting their promising practical applications as novel and efficient semiconductor photocatalysts for the water purification.     

Novel Bi<Subscript>12</Subscript>TiO<Subscript>20</Subscript>/g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> composite with enhanced photocatalytic performance through Z-scheme mechanism

Novel Bi₁₂TiO₂₀/g-C₃N₄ composite was successfully prepared with Bi₁₂TiO₂₀ nanoparticles embedded within the fluffy crumpled g-C₃N₄ nanosheets. Bi₁₂TiO₂₀/g-C₃N₄ composites exhibit superior photoactivity and stability. As compared with g-C₃N₄ and Bi₁₂TiO₂₀, the photocatalytic efficiency of Bi₁₂TiO₂₀/g-C₃N₄ is effectively enhanced about 1.8- and 4.9-fold, respectively. Based on the trapping experiment, ^·OH and ^·O₂^? radicals are the dominant reactive oxygen species involved in the photocatalytic process. The proposed Z-scheme mechanism of charge transfer markedly promotes the carriers’ migration and separation, leading to the enhanced photocatalytic performance.     

One-pot synthesis of isotype heterojunction g-C3N4-MU photocatalyst for effective tetracycline hydrochloride antibiotic and reactive orange 16 dye removal

The one-pot synthesis of g-C₃N₄-MU isotype heterojunction has been produced by the thermal polycondensation method by mixing different ratios of precursors between melamine and urea. The isotype heterojunction g-C₃N₄-MU samples were characterized by X-ray diffraction spectroscopy, scanning electron microscope and energy-dispersive X-ray-spectroscopy, UV–Visible diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The band-gap energy of these photocatalysts reveals that they can work well under visible light. The photocatalytic performance of the samples was investigated over the photodegradation of reactive orange-16 (RO-16) dye and tetracycline hydrochloride (TC-HCl) under visible light irradiation. The isotype heterojunction of g-C₃N₄-M6U10 showed the highest degradation of 95 and 85.6% for RO-16 and TC-HCl, respectively under irradiation time of 100 and 120 min. The major reactive species was identified as O₂^–. Moreover, the reusability of the photocatalyst was investigated up to 3 cycles with good efficiency. The present synthesized isotype heterojunction g-C₃N₄-MU could be applied as a facile pathway for synthesis and as an effective pathway to resolve various environmental problems.