Oxygen vacancies facilitated photocatalytic detoxification of three typical contaminants over graphene oxide surface embellished BiOCl photocatalysts

A conventional solvothermal way was used to synthesize graphene oxide (GO)/BiOCl photocatalytic nanomaterials with enhanced photocatalytic performance. Due to the introduction of GO, there are intuitive changes in morphology, indicating that GO can guide the growth of GO/BiOCl catalysts. The results of X-ray photoelectron spectroscopy (XPS) and Raman show that a strong chemical interaction occurs around GO and BiOCl. The results of trapping experiments show that O₂^– is the major active species. XPS analysis confirms that the 0.75% GO/BiOCl produces the highest level of oxygen vacancies (OVs). All the GO/BiOCl photocatalysts possess better photocatalytic properties than the neat BiOCl, and 0.5% GO/BiOCl exhibits the highest photoactivity. The photocatalytic activity of 0.5% GO/BiOCl composite for detoxification of rhodamine B (RhB) and tetracycline (TC) under visible light illumination is 4.6 and 6.3 times of that on the reference BiOCl, separately, the photocatalytic activity of 0.5% GO/BiOCl for detoxication of perfluorooctanoic acid (PFOA) is 1.25 times of that of the single BiOCl under UV light illumination, which can be credited to the high separation rate of carriers and the strong interaction between GO and BiOCl. Combining with the results, a separation and transfer mechanism of carriers was revealed.     

g-C3N4/BiOCl复合光催化剂作为2D/2D异质结用于光催化降解染料性能研究

为扩大BiOCl的太阳光吸收范围,获得更高效的光催化剂,本文通过水热法制备了石墨相氮化碳(g-C₃N₄)/BiOCl (2D/2D)复合光催化剂并对其进行详细表征。结构与形貌表征结果显示BiOCl纳米片沉积在层状g-C₃N₄表面,形成了2D/2D面-面复合结构;光电化学性质分析表明形成的异质结构能有效扩展光吸收频率范围,促进光生载流子分离和迁移,从而有利于光催化性能的提高。以500 W氙灯模拟太阳光源,光催化降解罗丹明B(RhB)的结果表明g-C₃N₄/BiOCl异质结的光催化降解活性远高于单纯的g-C₃N₄和BiOCl。其中9wt%g-C₃N₄/BiOCl表现出了最优越的光催化活性,在180 min内对RhB的降解率为94%,其表观速率常数K_app值为g-C₃N₄和BiOCl的5.7和3.6倍。同时对g-C₃N₄/BiOCl异质结的光催化机制展开研究,结合复合催化剂电子结构和自由基捕获实验提出了在染料敏化作用下RhB的光催化降解机制。      

Decoration of Au nanoparticles onto BiOCl sheets for enhanced photocatalytic performance under visible irradiation for the degradation of RhB dye

Plasmonic photocatalysts are promising candidates for use in the degradation of pollutants. Their ability to degrade a wide range of organic pollutants stems from key properties such as high visible light absorption, the ability to generate hot electrons and the formation of a Schottky barrier that facilitates effective separation of charge carriers. In the present work, we synthesised bismuth oxychloride sensitised with gold nanoparticles (NPs, 20–50 nm) via a two-step chemical process at low temperature. The fabricated Au/BiOCl powder was evaluated in the degradation of Rhodamine B (RhB) dye under visible light irradiation. The photocatalytic performance of the Au/BiOCl hybrid was almost double that of pristine BiOCl. This enhanced performance was attributed to electron transfer from BiOCl to Au via the formation of heterojunctions at the BiOCl/Au interface. Additionally, the surface plasmon resonance effect of the Au NPs provided high optical absorbance in the visible spectrum. TEM (transmission electron microscopy) analysis indicated the presence of polar (010) facets on the BiOCl sheets, which also contributed to dramatically improving their photocatalytic performance. The degradation time of the Au/BiOCl hybrid was 200 min compared with 320 min for pure BiOCl.     

Size-controlled BiOCl–RGO composites having enhanced photodegradative properties

Visible light-active bismuth oxychloride–reduced graphene oxide (BiOCl–RGO) composite photocatalysts were synthesised using a hydrothermal method at low temperature, and at a low cost. This approach reduced the recombination of electron–hole pairs and thereby provided more efficient photocatalysts. The size of BiOCl structure was controlled by polyvinylpyrrolidone (PVP) addition. Furthermore, formation of nanosized BiOCl sheets and BiOCl–RGO composites were confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Fabricated BiOCl–RGO composite with PVP exhibited better photocatalytic activity than pure BiOCl grown with and without PVP towards degradation of Rhodamine B (RhB). It was found that the composite photocatalyst degrades RhB completely within 310 min as compared with several hours for pure BiOCl. The improved photocatalytic performance of BiOCl–RGO composite was attributed to its high specific surface area (22.074 m² g^?1 and existence of polar surfaces, compared with 9.831 m² g^?1 for pure BiOCl). The analyses indicated that RGO helped to reduce recombination losses and improve electron transport. It also showed that presence of polar surfaces improved photocatalytic activity of BiOCl. Hence, BiOCl–RGO composite is a promising catalyst for the degradation of organic pollutants under visible light and could be used in applications such as water purification devices.     

Hydrothermal synthesis of sphere-like BiOCl using sodium lignosulphonate as surfactant and its application in visible light photocatalytic degradation of rodamine B

The BiOCl-SL was prepared by a simple hydrothermal reaction between Bi(NO₃)₃·5H₂O and KCl using sodium lignosulfonate (SL) as a structure-directing agent. The standard tetragonal structure of the BiOCl has been confirmed by X-ray powder diffraction. The scanning electron microscopy results revealed that a suitable amount of SL is favorable for the formation of hollow sphere-Like BiOCl. The fourier transform infrared spectroscopy (FT-IR) of the BiOCl-SL showed the BiOCl samples have been cleaned thoroughly, and the following photocatalytic experiment will not be affected by SL. In comparison with the pure BiOCl, the UV–Vis diffuse reflectance spectroscopy (UV–Vis-DRS) of the BiOCl-SL showed a red shift of absorption edge. The Brunauer–Emmett–Teller surface area measurement indicated that the surface area of BiOCl-SL is much bigger than that of pure BiOCl. The photocatalytic activity of BiOCl was tested on the degradation of Rodamine B (RhB) under visible light irradiation, and the result showed that the BiOCl-SL-0.3 had excellent photocatalytic activity for RhB after visible light irradiation for 2 h.     

高效碳量子点/BiOCl纳米复合材料用于光催化污染物降解

为了克服单纯BiOCl光谱吸收范围窄和载流子复合几率高的缺点, 本研究制备了一种具有高效光催化活性的碳量子点(CQDs)/BiOCl纳米复合材料。光催化降解罗丹明B染料实验表明CQDs/BiOCl纳米复合材料的光催化性能远优于单纯的BiOCl, 其光催化性能约为后者的3.4倍。当CQDs的复合量为7.1wt%时, 样品的光催化性能最佳, 能够在2 min之内将罗丹明B完全脱色, 而单纯的BiOCl在相同时间内对罗丹明B的降解率仅为29.5%。通过紫外-可见漫反射谱、光电化学测试以及自由基捕获实验揭示了CQDs/BiOCl纳米复合材料的光催化性能提升机理, 结果表明CQDs可以拓展BiOCl的可见光吸收范围, 这有利于增强其光捕获能力以及促进电子-空穴对的产生。除此之外, CQDs独特的上转换发光行为, 以及光诱导的电子转移能力提升了CQDs/BiOCl纳米复合材料光催化性能。     

Synthesis and photocatalytic activity of BiOCl/diatomite composite photocatalysts: Natural porous diatomite as photocatalyst support and dominant facets regulator

BiOCl/diatomite composite with enhanced photocatalytic property for the degradation of liquid Tetracycline hydrochloride (TC) and gaseous formaldehyde (HCHO) were successfully prepared by a facile hydrothermal method at different pH value. The structure and morphology characterizations of BiOCl/diatomite composite exhibit that diatomite not only acts as a natural porous support of photocatalyst but also acts as dominant facets regulator at pH = 3 when the doping amount is change, owing to the surface electrical property of the diatomite and interaction between diatomite and BiOCl. This interaction is certified by XPS and FT-IR which indicate that Bi in layer structure of [Bi₂O₂]²⁺ group interacts with the O in SiOSi bond when the formation of BiOCl with the participation of diatomite. The BET characterization confirms that the increasing amount of diatomite enables the composite with more reaction points for light harvest and molecule adsorption than pure BiOCl. Furthermore, TC and formaldehyde are targeted as degradation objects to test the photocatalytic property of BiOCl/diatomite composite. The optimum photocatalytic property are BiOCl(3–1.2) and BiOCl(12–0.6) at TC degradation and BiOCl(3–0.3) and BiOCl(12–0.6) at formaldehyde elimination, which is much better than that of pure diatomite or BiOCl. The difference of optimum photocatalysts in liquid and gaseous phase systems can be attributed to the photoelectric performances of BiOCl/diatomite composite, which were characterized by DRS, PL, transient photocurrents and the electrochemical impedance spectroscopy technique.     

Sonication-assisted deposition–precipitation synthesis of graphitic C<Subscript>3</Subscript>N<Subscript>4</Subscript>/BiOCl heterostructured photocatalysts with enhanced rhodamine B photodegradation activity

Novel two-dimensional graphitic carbon nitride (g-C₃N₄)/BiOCl nanosheets with excellent photodegradation activity towards rhodamine B (RhB) under visible light irradiation have been successfully synthesized by a sonication-assisted deposition–precipitation route. The composite nanosheets exhibited good dispersity and abundant contact interfaces, which led to the formation of p–n heterojunctions. Hybridization of g-C₃N₄ in the composites resulted in an extended absorption range and inhibited the recombination of the photoinduced charge carriers. Therefore, the two-dimensional heterostructure of the present compounds contributed to enhance their photocatalytic performances. In addition, the indirect photosensitization effect of RhB also influenced the photodegradation activity of BiOCl.     

Synthesis of heterostructured In2O3/BiOCl powders and their visible-light-driven photocatalytic activity for the degradation of Rhodamine B

Heterostructured In₂O₃/BiOCl powders were synthesized by chemical coprecipitation method at room temperature followed by thermal treatment at 400 °C for 2 h. The TEM results confirmed the formation of sheet-like BiOCl nanostructures with the thickness of ca. 5–7 nm. In order to investigate the effect of In₂O₃ on the photocatalytic activity of heterostructured powders, the amount of In₂O₃ was varied from 0 wt% to 14 wt%. Adsorption and photocatalytic activity of the samples were evaluated for the degradation of Rhodamine B (RhB) in the dark and under visible light irradiation, respectively. The heterostructured In₂O₃/BiOCl powders showed high adsorption capacity and enhanced photocatalytic activity compared to P25 and pure BiOCl. Based on the results obtained in this study, the mechanism for the enhancement of photocatalytic activity of heterostructured In₂O₃/BiOCl powders is discussed. 10 wt% In₂O₃/BiOCl composite also exhibited good cycle performance for the degradation of RhB under visible light irradiation.     

Size-constrained ultrathin BiOCl nanosheets@C composites with enhanced photocatalytic and photoelectrochemical performance

Size-constrained ultrathin BiOCl nanosheets@C composites were achieved by one-step hydrothermal route. It was found that the carbon coated on the surface of BiOCl nanosheets not only accelerated the separation of electrons and holes, but also restricted the outward growth of the BiOCl crystal structure to expose more active catalytic sites. In addition, the obtained composites have stable and close interface contact, beneficial for the structural stability of products as well as the rapid charge transfer. The average sheet thickness was in the range of 20–60 nm. Compared with the ability for pure BiOCl to degrade RhB, the degradation rate of the optimal composite can reach 100% within 15 min, while the corresponding photocurrent intensity could reach 5.6 μA·cm⁻², and its impedance value was also the smallest. The removal experiments of active substances showed that h⁺ and ∙O₂⁻ play important roles in the process of photocatalytic degradation. It can be expected that the resulted composites in this work can be used as potential materials for photocatalytic and photoelectrochemical applications.     

Synthesis of BiOCl/ZnMoO4 heterojunction with oxygen vacancy for enhanced photocatalytic activity

In this study, a novel oxygen vacancy-rich BiOCl/ZnMoO₄ composites were successfully prepared by a simple two-step method. Experimental results indicated that the content of BiOCl with oxygen vacancies played an important role in photocatalytic performance of OBZM heterostructures. OBZM-5 exhibited a highly enhanced photocatalytic activity under visible light irradiation compared to pure BiOCl, Ov-BiOCl, ZnMoO₄ and other OBZM composites, which can be attributed to the efficient separation and transfer of photogenerated charge carrier. The photocatalytic degradation efficiency of rhodamine B (RhB) can reach 99% within 40 min and almost all of norfloxacin (NOR) can be degradated after 100 min by OBZM-5. In addition, OBZM-5 displayed a good stability during the photocatalytic process, which favored a long-term use. Moreover, a possible photocatalytic mechanism was proposed based on the active species trapping experiments and electron spin resonance (ESR) tests, verifying that the photogenerated holes (h⁺) and ·O₂^? radicals were the dominating active species.

     

The Ag-based SPR effect drives effective degradation of organic pollutants by BiOCOOH/AgBr composites

The easy recombination of electron-hole pairs produced by monomeric photocatalysts under light exposure severely limits their application in wastewater treatment. Based on this, BiOCOOH/Ag/AgBr ternary photocatalysts in flower-like microspheres were controllably synthesized by precipitation photoreduction and characterized by various techniques. In addition, the effects of different molar ratio of BiOCOOH and AgBr, catalyst dose, pH and coexisting ions on the photocatalytic degradation of rhodamine B (RhB) and tetracycline (TC) were investigated. The results showed that the BOC/Ag/AgBr-0.5 composite exhibited excellent photocatalytic activity for the degradation of RhB and TC. The excellent photocatalytic activity was mainly attributed to the surface plasmon resonance (SPR) effect of metallic Ag and charge transfer mechanism between composites, thus promoting charge separation. The degradation efficiency of RhB and TC was 92.7% and 72.3% with the degradation rate constant of 0.073 and 0.023 under light irradiation of xenon lamp in 30 and 45 min, respectively, which was 6 and 2 times higher than that of BiOCOOH and AgBr. The stability studies showed that BOC/Ag/AgBr-0.5 maintained a high catalytic activity after four cycles. The results of radical capture experiments showed that h⁺ and ·O₂^– were the main reactive radicals, while ·OH played a secondary role in the photocatalytic system. Subsequently, a potential photocatalytic mechanism was proposed based on the experimental results.     

Facile preparation of Sn/BiOCl composite oxides and their photocatalytic performance

Sn-doped BiOCl (Sn/BiOCl) photocatalysts were synthesized by a precipitation method using Bi(NO₃)₃?·?5H₂O as a bismuth source, SnCl₂ as an Sn source, imidazole hydrochloride as a chlorine source, a solvent, and a template agent. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, surface area analysis (Brunauer, Emmett and Teller [BET]), and diffuse reflectance spectroscopy. The XRD results showed a greater increase in the peak intensity of Sn/BiOCl because of its high degree of crystallinity. The UV–Vis results indicated a redshift from 368?nm (BiOCl) to 418?nm (Sn/BiOCl), leading to the reduced band gap of BiOCl because of Sn doping in BiOCl. The Sn/BiOCl not only retained ultraviolet photocatalytic activity of BiOCl but also showed visible photocatalytic activity. The BET results showed that the surface area of Sn/BiOCl (23.35?m²?) was bigger than that of BiOCl (13.54?m²?g). The bigger surface show higher photocatalytic activity due to more contact opportunity between reactants. Hence, the increased photocatalytic activity of Sn/BiOCl in the degradation of rhodamine B can be attributed to a higher degree of crystallinity, larger surface area, and broader range of optical absorption. The Sn/BiOCl needed only 20?min under visible light and 40?min under ultraviolet light to completely degrade rhodamine B. Moreover, the photocatalytic experiment did not require any other chemical reagent such as H₂O₂. The microstructures of BiOCl and Sn/BiOCl ensured that the catalyst still has high recovery rate when it is reused. The microstructures of catalyst have a little of loss.     

响应可见光的高效催化剂BiOCl／AgCI的制备及其催化特性

以XBiCl3和AgNO3为原料,采用水解法成功地制备了BiOCl／AgCl复合催化剂,利用XRD、SEM、uV～VisDRS对样品进行了表征,以RhB为目标污染物,研究了不同初始nBi^3＋／nAg＋比、光源对光催化性能的影响,并探讨了样品的重复使用效率及光催化降解RhB的动力学行为,结果表明,初＋=anBi2＋／nAg＋比为100：1合成的样品具有最佳的光催化性能,在太阳光下仅照射15min其pH=6．5的20mg／LRhB溶液的脱色率即可达98．81％,而在卤素灯和紫外灯照射30min条件下,其脱色率分别为95．89％和11．63％。样品重复使用19次后,溶液脱色率仍高达95％,具有较好的稳定性。动力学研究表明,RhB光催化降解属表观一级动力学,反应符合Langmuir—Hinshelwood动力学方程,速控步为吸附反应。     

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.     

Relationship of structure and enhanced photocatalytic activity of S-scheme BiOCl/g-C3N4 heterojunction for xanthate removal under visible light

Constructing heterojunctions is an excellent way to enhance the photocatalytic property of semiconductors. Herein, a range of S-scheme BiOCl/g-C₃N₄ heterojunctions with varying mass ratios were designed using a facile hydrothermal route, and their photocatalytic ability was assessed by degrading the ethyl xanthate (EX) under visible light (λ > 400 nm). The results showed that the degradation efficiency of BiOCl/g-C₃N₄-0.1 heterojunction for EX was up to 91.2 % within 180 min, and its apparent rate constants (K_app) were 4.3 and 11 times greater than those of BiOCl and g-C₃N₄, respectively. The experimental and characterization results revealed that the excellent photocatalytic property was ascribed to the construction of S-scheme heterojunctions. Such structure not only enhanced the visible light response but also facilitated the efficient separation of photoinduced carriers with the S-scheme transfer route, retaining strong redox-capable holes and electrons to participate in surface reactions. Furthermore, the cycling experiments indicated that the fabricated photocatalysts have great recyclability and stability. Based on the results of active substance capture, the S-scheme charge transfer model was proposed and the photodegradation mechanism of EX was reasonably elucidated. Overall, this work offers some theoretical direction for the design and construction of S-scheme heterojunctions with superior visible-light-driven photocatalytic performance.     

BiOCl nano/microstructures on substrates: Synthesis and photocatalytic properties

Bismuth oxycholoride (BiOCl) nano/microstructures, including flake and nanowire arrays, were successfully synthesized on Anodic Aluminum Oxide (AAO) templates via sol-gel combined with the vacuum air-extraction method. The flakes are almost vertically aligned on the surface, but nanowires at a lower sol concentration are aligned along the channels. A possible formation mechanism is proposed. Furthermore, the photocatalytic activity of the BiOCl nano/microstructures is investigated by photocatalytic decomposition of Rhodamine B (Rh B) dye under UV-Visible light irradiation. Compared with the BiOCl flake-like film on the glass substrate, where the flakes are horizontally oriented on the surface, the vertically aligned flake and nanowire arrays on AAO templates, have higher photocatalytic efficiency.     

Nanoarchitectonics of chlorophyll and Mg co-modified hierarchical BiOCl microsphere as an efficient photocatalyst for CO2 reduction and ciprofloxacin degradation

It is of great significance to develop an efficient photocatalyst through simple methods for solar energy conversion and environmental pollution treatment. In this research, chlorophyll (Chl) and Mg co-modified hierarchical BiOCl microsphere photocatalyst with high performance was synthesized using a simple low temperature wet-chemical method. The synthesized photocatalyst with the optimal content of Chl and Mg showed superior photocatalytic performance for CO₂ reduction, where the maximum yield of methanol was 100.2 µmol/(h·g_cat), which was about three times superior than that of pure BiOCl. Besides, the Chl-Mg/BiOCl also showed high performance (93.7%) for degradation of ciprofloxacin (CIP, a kind of antibiotic). Various characterization techniques were applied to determine the structure and evaluate the origin of the improved performance of Chl-Mg/BiOCl. Meanwhile, a possible mechanism for the excellent photocatalytic performance of Chl-Mg/BiOCl was proposed. Notably, Chl on the surface of BiOCl can lead to the formation of singlet state of Chl-Mg* after absorbing light and act as an electron donor which can enhance the stability and activity of the photocatalyst. What’s more, Mg not only acts as an electron capture site to inhibit the photogenerated carrier recombination, but also forms a complex with Chl to improve the stability of catalyst. This study would represent a promising candidate organic–inorganic hybrid photocatalyst for solar energy conversion and antibiotic pollution treatment.     

研磨-焙烧法制备La2O3/BiOCl复合光催化剂及其对高浓度染料降解性能

首先利用沉淀法合成了BiOCl纳米片, 然后利用研磨-焙烧法将La₂O₃纳米颗粒复合到BiOCl纳米片中, 制备了一系列La₂O₃/BiOCl复合光催化剂(La₂O₃: 1wt%、2wt%、4wt%、8wt%)。运用X射线粉末衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、光电子能谱(XPS)、紫外-可见漫反射光谱(UV-Vis DRS)、傅里叶红外光谱(FT-IR)和光致发光(PL)谱等对样品的晶相、光吸收和表面性能等进行了表征。以紫外灯(λ = 254 nm)为光源, 评价了所制备样品光催化降解高浓度染料酸性橙II(40×10^-6)的活性。结果表明, 经过研磨-焙烧后该系列催化剂均具有较好的结晶性能, 同时2~5 nm的La₂O₃纳米粒子粘附在BiOCl纳米片表面。200℃焙烧制备的1wt%La₂O₃/BiOCl催化剂具有丰富的表面羟基, 对染料表现出较强的吸附性能。该催化剂表现了最高的光催化活性, 活性为纯BiOCl的2.4倍。另外, La₂O₃/BiOCl中的La³⁺提供的氧化-还原势阱可能捕获光生电子, 从而阻止了光生电子(e^-)和空穴(h⁺)的复合, 有利于光催化活性的提高。     

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.