Construction of CoTiO3/BiOI p-n heterojunction with nanosheets-on microrods structure for enhanced photocatalytic degradation of organic pollutions

Herein, a novel CoTiO₃/BiOI (CTOB) p-n heterojunction with nanosheets-on microrods structure were prepared via a simple coprecipitation method for the first time. The catalysts were carefully characterized by various instruments. The CTOB heterostructures display improved photocatalytic performance towards RhB degradation. Among CTOB composites, CTOB-15 exhibits the optimal photocatalytic performance. Moreover, CTOB-15 also shows enhanced photocatalytic activity for MO and TC degradation compared to bare catalysts. The degradation rate constants for RhB and MO by CTOB-15 heterostructure are ca 1.6 and 1.4-fold higher than bare BiOI. The improved photocatalytic performance could be on account of the efficient separation of photoinduced carriers as well as enhanced light absorbance. Trapping experiments indicates that holes (h⁺) and superoxide anion radical (O₂^–) play a significant role in the removal of RhB by CTOB composites. The excellent photocatalytic activity and stability make it a promising photocatalyst in environmental remediation.     

Preparation of Ag-TiO2 hollow structures with enhanced photocatalytic activity

This paper describes a one-pot surfactant-assisted hydrothermal method for the synthesis of Ag-TiO₂ composite hollow structures with high photocatalytic activity. TEM measurement reveals that the sample is composed of hollow spheres and their tube-like aggregates. The surfactant cetyltrimethylammonium bromide (CTAB) plays a key role in the construction of the Ag-TiO₂ hollow structures. The Ag-TiO₂ hollow structures showed effective photocatalytic activity for the decomposition of methyl orange.     

原位构建P-N结复合材料及其可见光光催化性能

提高光催化过程中电子和空穴的提取和分离速率是提高光催化剂催化性能的关键技术之一。用浓硫酸剥离体相氮化碳得到石墨相g-C₃N₄,采用原位生长法制备花状g-C₃N₄/BiOBr P-N结复合材料,研究pH值对复合材料形貌的影响。利用XRD,SEM,EDS,TEM,UV-vis, BET等测试技术对所得样品的形貌、结构进行表征,讨论样品的光催化性能。结果表明:在g-C₃N₄/BiOBr复合材料内g-C₃N₄的[002]晶面和BiOBr的[001]晶面之间形成了异质结,可加速光生电子(e^-)和空穴(h⁺)的提取和分离。BiOBr和g-C₃N₄/BiOBr的禁带宽度分别为2.75,2.71 eV,复合材料的带隙减小,对可见光的吸收范围增强。BiOBr和g-C₃N₄/BiOBr复合材料的比表面积分别为1.27,6.43 m²/g,比表面积增大,增加催化反应活性位点。复合材料g-C₃N₄/BiOBr的光催化性能比纯g-C₃N₄和BiOBr更好,且重复使用效果佳。pH=8时制备的g-C₃N₄/BiOBr复合材料光催化效果最好,此时,对橙黄G、罗丹明B、甲基橙的光催化降解效率分别为91.00%,95.51%,96.72%。     

Fabrication of novel ZnO/BiOBr/C-Dots nanocomposites with considerable photocatalytic performances in removal of organic pollutants under visible light

In this study, ternary ZnO/BiOBr/C-Dots photocatalysts were successfully prepared by a simple strategy. Then, their characteristics such as structure, morphology, chemical, optical, textural, and photocatalytic performances were fully investigated. This study demonstrated that the ZnO/BiOBr/C-Dots nanocomposites showed remarkably increased photocatalytic performances compared with the ZnO and ZnO/BiOBr samples. In decolorization of RhB upon visible light, the highest activity was obtained when the volume of C-Dots was 0.25?mL, which was about 39.7 and 2.7?times premier than the ZnO and ZnO/BiOBr photocatalysts, respectively. In the ternary nanocomposites, the increased performance was mainly ascribed to the formed heterojunction between the counterparts, up conversion characteristics of C-Dots, and visible-light harvesting ability of BiOBr. The reactive species trapping experiments proved that O₂^? was the major species involved in the photocatalysis reaction. At last, the ternary nanocomposite displayed remarkable stability for recycling runs.     

Rapid,simple and low-cost fabrication of BiOBr ultrathin nanocrystals with enhanced visible light photocatalytic activity

BiOBr ultrathin nanocrystals were prepared by a rapid, simple and low-cost route, and characterised by X-ray diffraction, scanning electron microscope, transmission electron microscopy, energy dispersive X-ray, UV–vis diffuse reflectance spectroscopy and electrochemical impedance spectroscopy analyses. The size of the resulting BiOBr ultrathin nanocrystals is about 60–100 nm in width and 15–20 nm in thickness. The photocatalytic activity of the samples was evaluated in terms of the degradation of RhB. Compared with BiOBr three-dimensional microspheres and P₂₅-TiO₂, the BiOBr ultrathin nanocrystals exhibited the best visible-light-induced photocatalytic activity.     

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.     

The excellent photocatalytic activity of novel Cs3PW12O40/WO3 composite toward the degradation of rhodamine B

In this paper, a simple one-pot thermal decomposition method was successfully used to synthesize a novel Cs₃PW₁₂O₄₀/WO₃ composite for the first time. The synthesized composite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), FTIR, diffuse reflectance spectroscopy (DRS) and N₂ adsorption-desorption techniques. The photocatalytic activity to degrade RhB molecules over Cs₃PW₁₂O₄₀/WO₃ composite was evaluated under xenon light irradiation. The results indicated the complete degradation of RhB molecules over Cs₃PW₁₂O₄₀/WO₃ composite after 30?min irradiation. However, the photocatalytic degradation of RhB over WO₃ and Cs₃PW₁₂O₄₀ after 80?min light irradiation are nearly 52%, and 68%, respectively. The enhanced photocatalytic activity of Cs₃PW₁₂O₄₀/WO₃ composite compared with WO₃, and Cs₃PW₁₂O₄₀ was ascribed to the strong interaction between WO₃ and Cs₃PW₁₂O₄₀, which effectively reduces the recombination of photogenerated electron-hole pairs. Based on experimental results, the possible mechanism of photocatalytic reactions on the Cs₃PW₁₂O₄₀/WO₃ composite photocatalyst was investigated, and the hydroxyl radical (OH) and superoxide radical (O₂^?) were determined as the main active species in the photocatalytic degradation of RhB over Cs₃PW₁₂O₄₀/WO₃ composite.     

Synthesis of fluorescent carbon quantum dots from aqua mesophase pitch and their photocatalytic degradation activity of organic dyes

A synthesis strategy of fluorescent carbon quantum dots (CQDs) with high quantum yield (QY) using aqua mesophase pitch (AMP) as the carbon source has been developed via the hydrothermal method in this study. The hydrothermal temperature and soaking time have important effects on the morphology and QY of CQDs. As-prepared CQDs at 120 °C holding for 24 h (CQDs-120-24) have the uniform size of about 2.8 nm, and the QY can reach 27.6%. The obtained CQDs are successfully modified with ammonia and thionyl chloride, respectively, and they exhibit an excellent photocatalytic performance on degrading rhodamine B (Rh B), methyl blue (MB) and indigo carmine (IC). Importantly, the degradation percentage of N-CQDs on Rh B under natural light for 4 h reaches 97% with the degradation rate constant of 0.02463 min⁻¹ and it can maintain 93% after repetitively used 5 times. The results indicate that these as-prepared CQDs have the potential application in degrading organic dyes.     

Solar photocatalytic degradation of isoproturon over TiO2/H-MOR composite systems

The photocatalytic degradation and mineralization of isoproturon herbicide was investigated in aqueous solution containing TiO₂ over H-mordenite (H-MOR) photocatalysts under solar light. The catalysts are characterized by X-ray diffraction (XRD), UV–Vis diffused reflectance spectra (UV–Vis DRS), Fourier transform-infra red spectra (FT-IR) and scanning electron microscopy (SEM) techniques. The effect of TiO₂, H-MOR support and different wt% of TiO₂ over the support on the photocatalytic degradation and influence of parameters such as TiO₂ loading, catalyst amount, pH and initial concentration of isoproturon on degradation are evaluated. 15 wt% TiO₂/H-MOR composite is found to be optimum. The degradation reaction follows pseudo-first order kinetics and is discussed in terms of Langmuir–Hinshelwood (L–H) kinetic model. The extent of isoproturon mineralization studied with chemical oxygen demand (COD) and total organic carbon (TOC) measurements and 80% mineralization occurred in 5 h. A plausible mechanism is proposed based on the intermediates identified by liquid chromatography–mass spectroscopy (LC–MS).     

One-pot synthesis of ZnO/Ag nanospheres with enhanced photocatalytic activity

ZnO/Ag composite nanospheres with an average diameter of about 440 nm, were synthesized through a facile one-pot solvothermal reaction, using a kind of biomolecular sodium alginate as template, H₂O and diethanolamine as solvents, followed by the assembly of ZnO and Ag nanoparticles in-situly produced. The composite spheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy disperse X-ray spectrum. Moreover, the results showed that the as-made ZnO/Ag assembled nanospheres exhibited better photocatalytic performance than the pure ZnO nanoparticles and this one-pot synthesis method has great potential to be extended for the synthesis of other metallic oxide/metal spheres.     

Self-assembly of the Ag deposited ZnO/carbon nanospheres: A resourceful photocatalyst for efficient photocatalytic degradation of methylene blue dye in water

Carbon nanospheres (CNSs) are synthesized by pyrolysis of benzene at 1000?°C. Various UV-light photocatalysts of ZnO/CNSs and Ag-ZnO/CNSs (AZCN) composites are synthesized on the surface of CNSs using a facile chemical precipitation method. Morphological and optical properties of the as-synthesized photocatalysts are characterized by scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, UV-Vis spectroscopy, photoluminescence and Raman spectroscopy. Photocatalytic degradation efficiency of methylene blue dye is investigated to examine the photocatalytic activity of synthesized photocatalysts. It is found that as-synthesized ZnO/CNSs composite can degrade higher methylene blue dye (～85.6%) after 25?min of UV irradiation in comparison with that of CNSs. A prominent improvement in the photodegradation is attained by depositing metal (Ag) particles on the surface of ZnO/CNSs composite. AZCN composite displays the enhanced photocatalytic degradation performance (～95% after 15?min of UV light) in high concentration of methylene blue dye. Furthermore, stability performance is studied by recycling the AZCN composite photocatalyst. It is found that the photocatalytic activity of AZCN composite is only slightly decreased even after five cycles. Present work demonstrates that AZCN composite show a great potential in the treatment of organic pollutants for wastewater treatment.     

Magnetically separable composite photocatalyst with enhanced photocatalytic activity

A novel magnetically separable composite photocatalyst, anatase titania-coated magnetic activated carbon (TMAC), was prepared in this article. In the synthesis, magnetic activated carbon (MAC) was firstly obtained by adsorbing magnetic Fe₃O₄ nanoparticles onto the activated carbon (AC), and then the obtained MAC was directly coated by anatase titania nanoparticles prepared at low temperature (i.e. 75 °C). The prepared samples were characterized by XRD, SEM and vibrating sample magnetometer (VSM). The composite photocatalyst can be easily separated from solution by a magnet, its photocatalytic activity in degradation of phenol in aqueous solution also has dramatic enhancement compared to that of the neat titania.     

Synthesis of TiO2 nanotubes coupled with CdS nanoparticles and production of hydrogen by photocatalytic water decomposition

The CdS/TiO₂NTs composite was prepared by a simple two-step chemical solution routes to directly transfer trititanate nanotubes to TiO₂NTs and simultaneously coupled with CdS nanoparticles. The results of XRD, TEM, Diffuse reflectance UV-Visible absorption spectra revealed that the CdS nanoparticles were homogeneously embedded on the surface of TiO₂NTs and the absorption spectrum of TiO₂NTs was extended to visible region. The activity of hydrogen production by photocatalytic water decomposition for the CdS/TiO₂NTs composite was examined under visible light irradiation (λ > 400 nm) and the quantity of H₂ evolution was ca. 1708 μL/g for 6 h.     

Ternary novel TiO2/MgBi2O6/Bi2O3 nanocomposites with n-n-p heterojunctions: Impressive visible-light-triggered photocatalytic degradation of tetracycline

A series of novel ternary TiO₂/MgBi₂O₆/Bi₂O₃ nanocomposites were synthesized by a facile hydrothermal method. The ternary nanocomposites were characterized by XRD, FESEM, HRTEM, EDX, PL, EIS, Photocurrent, UV–vis DRS, BET, XPS, Raman, and FT-IR analyses. The photocatalytic performance of TiO₂ for the degradation of tetracycline antibiotic after combining with MgBi₂O₆/Bi₂O₃ was significantly improved, which is 46.1 and 18.5 times higher than pristine TiO₂ and MgBi₂O₆/Bi₂O₃ photocatalysts, respectively. Furthermore, the ternary photocatalyst efficiently degraded MO, RhB, and MB dye pollutants, which is 22.5, 30.4, and 30.0 as high as TiO₂ and 11.2, 14.4, and 17.8 folds larger than MgBi₂O₆/Bi₂O₃ photocatalysts, respectively. The photoluminescence and electrochemical analyses confirmed promoted separation and facile transfer of the charges thanks to construction of n-n-p heterojunctions among n-TiO₂, n-MgBi₂O₆, and p-Bi₂O₃ components and more production of charge carriers due to integration of small band gap MgBi₂O₆ and Bi₂O₃ components with wide band gap TiO₂.     

Electrospinning of CeO2-ZnO composite nanofibers and their photocatalytic property

CeO₂-ZnO composite nanofibers were fabricated via the electrospinning technique using zinc acetate and cerium nitrate as the precursors, poly(vinylpyrrolidone) as the fiber template, and 2:1(v/v) ethanol/water mixtures as the co-solvent, followed by thermal treatment at 600 °C for 3 h. Various characterization methods were employed to investigate the morphologies and structures of the nanofibers. The calcined composite nanofibers showed a continuous line feature with an average diameter of 46 nm composed of 15 ± 3 nm CeO₂ and ZnO nanoparticles. Photocatalytic activity experiments showed that the Rhodamine B was almost completely decomposed when it was catalyzed by CeO₂-ZnO nanofibers within 3 h, while only 17.4% and 82.3% were decomposed under catalysis by CeO₂ and ZnO nanofibers respectively. Such CeO₂-ZnO composite nanofibers could have potential applications in the treatment of organic-polluted water.     

Porous SrTiO3 spheres with enhanced photocatalytic performance

Porous SrTiO₃ spheres were successfully synthesized by a convenient hydrothermal method, employing SrCl₂ as Sr source and titanate nanotube as Ti precursor. In this reaction, when short titanate nanotube was used as Ti precursor, porous SrTiO₃ spheres were generated for the aggregation of the nanotube@SrTiO₃ heteronanostructure. Whereas long titanate nanowire was used as the Ti precursor, solid SrTiO₃ spheres were obtained due to the SrTiO₃ which grows up gradually on the titanate nanowire. The morphology and the pore size of the SrTiO₃ sphere structures can be easily controlled by simply adjusting the reaction time, reaction temperature and the Ti precursor. The porous SrTiO₃ spheres exhibited enhanced photocatalytic activity which could achieve 100% degradation of Rhodamine B with a UV irradiation for 20 min.     

Sepiolite/Cu2O/Cu photocatalyst: Preparation and high performance for degradation of organic dye

A novel ternary sepiolite/Cu₂O/Cu (SCC) nanocomposite was successfully synthesized by a facile one-pot method. The Cu₂O/Cu nanoparticles in the SCC nanocomposite are well dispersed on the sepiolite surface. It exhibited enhanced photocatalytic performance in the degradation of congo red (CR), remarkably superior to that of Cu₂O or Cu₂O/Cu nanoparticles. Elemental copper in the SCC serves as a good electron acceptor to promote the transfer of photo-generated electrons in Cu2O and suppress the recombination of the photo-generated electrons and holes of the composite. The enhanced photocatalytic efficiency is attributed to the synergistic effect of sepiolite and Cu₂O/Cu. This type of SCC nanocomposites is a promising candidate as photocatalytic material for environmental protection.     

Preparation and photocatalytic activity of hollow ZnO and ZnO-CuO composite spheres

ZnO and ZnO-CuO composite hollow spheres were fabricated by using colloidal carbon spheres as templates. The morphology, structure and chemical composition of the as-prepared samples were investigated using field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The photocatalytic activity of the hollow spherical products was evaluated by photocatalytic degradation of methylene blue (MB) aqueous solution at ambient temperature. The results indicated that the ZnO-CuO composite hollow spheres display higher photocatalytic efficiency than pure hollow ZnO products. The related photocatalytic mechanism was discussed based on the microstructure and properties of the ZnO and ZnO-CuO composite hollow spheres. The facile strategy for the preparation of ZnO-CuO hollow nanostructures can be applicable to the synthesis of other composite hollow spheres.     

Parameters affecting the photocatalytic degradation of dyes using TiO2-based photocatalysts: A review

This paper presents the review of the effects of operating parameters on the photocatalytic degradation of textile dyes using TiO₂-based photocatalysts. It further examines various methods used in the preparations of the considered photocatalysts. The findings revealed that various parameters, such as the initial pH of the solution to be degraded, oxidizing agents, temperature at which the catalysts must be calcined, dopant(s) content and catalyst loading exert their individual influence on the photocatalytic degradation of any dye in wastewaters. It was also found out that sol–gel method is widely used in the production of TiO₂-based photocatalysts because of the advantage derived from its ability to synthesize nanosized crystallized powder of the photocatalysts of high purity at relatively low temperature.     

PH-induced structural evolution,photodegradation mechanism and application of bismuth molybdate photocatalyst

In this work, we have elucidated the pH-induced structural evolution of bismuth molybdate photocatalyst based on a hydrothermal synthesis route. With increasing the pH value of precursor solution, pure Bi₂MoO₆ was synthesized at pH 2–5, Bi₂MoO₆-Bi₄MoO₉ mixture was obtained at pH 7–9, pure Bi₄MoO₉ was obtained at pH 11, and pure α-Bi₂O₃ was derived at pH 13. The as-derived samples mainly present particle-like shapes but with different particle sizes (except the observation of Bi₂MoO₆ nanowires in sample S-pH9). The photocatalytic performances between the samples were compared via the degradation of methylene blue (MB) under irradiation of simulated sunlight. The Bi₂MoO₆ sample synthesized at pH 2 exhibited the highest photodegradation performance (η(30 min) = 89.8 %, k_app = 0.05007 min^?1) among the samples. The underlying photocatalytic mechanism and degradation pathways of MB were systematically analyzed. Moreover, the photodegradation performance of the Bi₂MoO₆ photocatalyst was further evaluated at different acidic-alkaline environments as well as in degrading various color and colorless organic pollutants, which provides an important insight into its practical application.