BiOCl/UiO‐66 composite with enhanced performance for photo‐assisted degradation of dye from water

Semiconductor‐based photocatalysis is an environmental friendly and cost‐effective technique for water treatment. Due to their unique properties, metal–organic frameworks (MOFs) are considered as ideal platform to develop composite photocatalyst. In this study, Bismuth oxychloride (BiOCl) was first attempt to be incorporated with highly stable MOFs, UiO‐66(Zr) by hydrothermal reaction. Different characterization methods including X‐ray diffraction, Scanning electron microscopy, Fourier transform infrared spectroscope, X‐ray photoelectron spectroscopy had been used to prove the successful synthesis of composite photocatalyst. The resultant BiOCl/UiO‐66 composite showed higher photodegradation performance of Rhodamine B (RhB) under ultraviolet and visible light irradiation than that of pristine materials and their mechanically mixed sample. In addition, the composite exhibited good structural stability and reusability. The photocatalytic mechanism of RhB degradation over the composite under visible light proceeded via a photosensitization process. A better adsorptivity of RhB and effective electron transfer within the hybrid material might be responsible for the enhanced photocatalytic performance.     

超声波辐射快速合成高光催化性能的BiOCl(Br)纳米片

在室温条件下,利用超声波辐射方法快速合成了四方状BiOCl(BiOBr)纳米片光催化剂。应用N2-物理吸附、X射线粉末衍射、扫描电镜、透射电镜、紫外可见光谱等手段对催化剂进行了表征,并以波长为λ=365 nm的紫外光和420 nm<λ<660 nm的可见光为光源,评价了该催化剂光催化降解酸性橙Ⅱ的活性。表征结果表明,超声波辐射可加速BiOCl和BiOBr晶化过程,显著提高BiOCl和BiOBr的结晶度,并使其晶粒发生细化,提高催化剂的比表面积。活性测试表明,声化学合成样品的光催化活性优于普通搅拌制备的样品。其中BiOCl的紫外光催化活性高于商业TiO2(P25)光催化剂。     

共沉淀法制备稀土Ce掺杂的纳米ZnO及其光催化降解染料的性能

以六水合硝酸锌和六水合硝酸铈?髥为原料,通过共沉淀法制备了一系列稀土Ce掺杂的纳米ZnO,并采用X射线粉末衍射(XRD)、傅里叶红外光谱(IR)、扫描电镜(SEM)、X射线能谱分析(EDS)、紫外可见漫反射光谱对其进行了全面表征。部分样品还通过X射线光电子能谱(XPS)和光致荧光光谱(PL)进行了进一步分析。分别在日光和紫外光条件下,对这一系列Ce掺杂的ZnO进行了光催化降解亚甲基蓝的性能研究,得出当Ce的掺杂量为3%(n/n)时(ZnO-3%Ce),其光催化活性最佳,光催化降解亚甲基蓝的效率均超过98%。选取ZnO-3%Ce作为催化剂,分别进一步考察其在日光和紫外光下对罗丹明B和甲基橙的光催化降解性能。研究结果表明,ZnO-3%Ce在日光和紫外光下均表现出较好的光催化降解效果,体现出良好的光降解普适性。日光下光降解效率顺序为:亚甲基蓝>罗丹明B>甲基橙,而紫外光下降解效率顺序为:罗丹明B>亚甲基蓝>甲基橙。最后,我们研究了催化剂ZnO-3%Ce的循环利用及稳定性性能。实验结果表明:该催化剂循环使用3次之后,光催化效率仍然稳定在97%以上,并且其结构和组成保持不变,体现出优异的稳定性和应用前景。     

Room Temperature Synthesis and Photocatalytic Activity of Magnetically Recoverable Fe3O4/BiOCl Nanocomposite Photocatalysts

Magnetically recoverable Fe₃O₄/BiOCl nanocomposite photocatalysts were fabricated by a simple chemical coprecipitation method at room temperature. The amount of Fe₃O₄ incorporated into BiOCl was varied from 0 to 20 wt%. The as-synthesized samples were characterized by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, UV–Vis diffuse reflectance spectroscopy, and vibrating sample magnetometer. The obtained results show that the as-synthesized samples mainly contain both crystalline phases (Fe₃O₄ and BiOCl) and are composed of flower-like nanostructures. Compared to UV light-responsive BiOCl, all the nanocomposite photocatalysts show a strong light absorbance in the range of 250–800 nm, demonstrating that the Fe₃O₄/BiOCl nanocomposites can respond to visible as well as UV light. Moreover, visible light absorbance was increased with the increase in the Fe₃O₄ amount in the composite. The photocatalytic activity of nanocomposite photocatalysts was evaluated by the photodegradation of Rhodamine B (RhB) over the samples under visible light irradiation. The 10 wt% Fe₃O₄/BiOCl nanocomposite photocatalyst shows the highest photocatalytic efficiency among the samples. The Fe₃O₄/BiOCl nanocomposite photocatalyst was stable under visible light irradiation to efficiently degrade RhB molecules after five cycles and could be easily recovered with a magnet after each cycle.     

Synthesis and photocatalytic properties of sunlight-responsive BiOBr–CoWO4 heterostructured nanocomposites

Efficient sunlight-responsive BiOBr–CoWO₄ heterostructured nanocomposite photocatalysts were prepared via a chemical precipitation route at 100°C in 4 hours. The prepared BiOBr–CoWO₄ heterostructures were characterized for phase identification, chemical composition, surface morphology, optical properties and surface area using various techniques. The X-ray diffraction pattern of the BiOBr–CoWO₄ nanocomposite was composed of diffraction peaks equivalent to both the tetragonal phase of BiOBr and the monoclinic phase of CoWO₄ nanoparticles. X-ray photoelectron spectral study of the BiOBr–CoWO₄ nanocomposite revealed orbitals of both BiOBr and CoWO₄ compounds. Transmission electron microscopy images revealed that spherical particles of CoWO₄ (20–25 nm) were dispersed on the surface of BiOBr. UV–visible–near-infrared spectral study of the BiOBr–CoWO₄ nanocomposite showed good visible-light absorption. Among the manufactured materials, BiOBr–CoWO₄-2 nanocomposite showed better charge carrier separation efficiency, as demonstrated by photoluminescence and time-resolved fluorescence. To study the practical utility of the prepared materials, their photocatalytic capability was examined for the degradation of rhodamine B (RhB) aqueous solution under sunlight irradiation. The photodegradation results showed that BiOBr–CoWO₄-2 nanocomposite degraded 98.69% RhB solution and the degradation constant was 0.067 min⁻¹, which was 5.6 and 22.5 times larger than that of pure BiOBr and CoWO₄ nanoparticles, respectively, after 60 minutes of sunlight irradiation. The superior photoactivity was facilitated by electron–hole pair separation and transfer driven by the heterostructure interface between BiOBr particles and CoWO₄ nanoparticles. The removal of RhB was initiated by photogenerated h⁺, O₂^{• −} and ^•OH reactive species based on the scavenger effect.     

Preparation and measurement of properties of BiOBr/BiOCl/PANI ternary nanocomposite for highly efficient visible light photocatalytic applications

In this paper, we report the synthesis of the BiOBr/BiOCl/PANI ternary nanocomposite using a simple co-precipitation method. The modified photocatalyst produced was characterized by the FT-IR, FE-SEM equipped with EDS (as a Map), TEM, XRD, PL, Raman, and UV–Vis DRS analytical techniques. The synergetic effect of PANI and surface defects in nanoplates can prolong the recombination rate of photo-generated charge carriers. Thus, photocatalytic and photoelectrochemical activities of samples have been studied. Then, the methyl orange (MO) degradation performance of PANI/BiOBr and BiOBr/BiOCl/PANI was investigated under visible light irradiation. The lamp used to simulate sunlight in this photocatalytic study process was power down white light (5-W LED), less reported. The results got exhibited that the as-prepared BiOBr/BiOCl/PANI (90:10, Bi:PANI) nanocomposite showed a higher photocatalytic efficiency. Based on the scavenger tests, ^·O₂^? played a significant role in the degradation of MO. The connection between BiOBr, BiOCl, and PANI improved photocatalytic activity, which enhanced migration rate of the photo-generated electrons besides limiting the recombination of photo-generated electron–hole pairs.

     

NaF浸泡处理对BiOBr光催化降解有机染料罗丹明B的影响

以五水硝酸铋(Bi(NO_3)_3·5H_2O)和溴代十六烷基吡啶(CPB)为原料,通过水热法合成溴氧化铋(BiOBr)光催化剂,并在pH=3.3的条件下分别用0.01 mol/L、0.1 mol/L、0.3 mol/L NaF溶液对其进行浸泡氟化处理得新催化剂BiOBr-F_(0.01)、BiOBr-F_(0.1)和BiOBr-F_(0.3).运用XRD(X-射线衍射)、SEM(扫描电镜)、UV-Vis DRS(紫外-可见漫反射光谱)、XPS(X-射线光电子能谱)、FL(荧光光谱)等技术对催化剂的物理结构及性质进行表征并研究了其在可见光(λ≥420 nm)下对有机染料罗丹明B(Rhodamine B,RhB)的催化降解活性.结果表明,随着NaF浓度增加,催化剂的结构及性质均发生一定程度的改变.氟化使得BiOBr对RhB的矿化能力减弱;但BiOBr-F_(0.1)使RhB褪色加快.RhB在降解过程中涉及到超氧自由基(O_2~(·-))、羟基自由基(·OH)及空穴(h~+)氧化,矿化率减小归因于活性物种产量降低,BiOBr-F_(0.1)使褪色加速则是加快了RhB的脱烷基过程,使最大吸收峰快速蓝移.     

氯氧化铋催化剂的电子结构调控及其光催化性能研究

以不同Bi/Cl摩尔比例为原料设计合成了一系列BiOCl半导体催化材料。扫描电子显微镜、XRD衍射峰拟合等分析结果显示,Bi/Cl比例的改变对BiOCl的形貌、表面结构、微观电子结构均具有一定的调控作用。以Bi/Cl = 1 : 1为原料合成的BiOCl光催化剂具有最窄的带隙值（Eg=3.18 eV）,使得其具有较强的的光响应能力。光催化去除罗丹明B（RhB）结果表明,随着Bi/Cl摩尔比例的减小,BiOCl的催化性能呈现先增强后减弱的趋势。Bi/Cl = 1 : 1样品具有最优的催化活性,源于其较优异的光吸收性能以及特殊的表面特性。光催化机理研究表明,光催化去除RhB的过程中,起作用的活性物质主要为光生电子、空穴以及半导体表面产生的超氧自由基。     

Adsorption factor and photocatalytic degradation of dye-constituent aromatics on the surface of TiO2 in the presence of phosphate anions

The photocatalytic degradation for some kinds of dye-constituent aromatics with TiO₂ in the presence of phosphate anions in aqueous dispersion was investigated under both visible light (λ>480 nm) and UV irradiation. The influences of phosphate anion upon the degradation of organics under these different conditions was revealed by the measurement of point of zero ξ-potential (P _ZC) of TiO₂, UV-VIS spectra, HPLC and LC-MS. The adsorption and photodegradation of some organics, which adsorb on the surface of TiO₂ by a dominating group bearing a positive charge, was enhanced, while that of others, which adsorb on the surface of TiO₂ by a dominating group bearing negative charge, was depressed by the presence of phosphate anions under UV irradiation at the experimental conditions (pH 4.3). It was confirmed that better adsorption of organics on the surface of TiO₂ had an advantage in their photocatalytic degradation under UV irradiation. On the other hand, although the adsorption of rhodamine B (RhB) and methylene Blue (MB) markedly increased, their degradation under visible light irradiation was depressed in the presence of phosphate anions. It is suggested that phosphate anion greatly blocked the electron transfer from excited RhB and MB molecules as RhB and MB molecules predominantly adsorbed on the surface of TiO₂ through the electrostatic interaction with surface adsorbed phosphate anions.     

Carbon nanotubes as photoprotectors of organic dyes: reversible photoreaction instead of permanent photo-oxidation

In this paper we report that single-walled carbon nanotubes (SWNTs) can protect surface adsorbed Rhodamine B (RhB) molecules from permanent photo-oxidation via a reversible reaction. Upon strong light irradiation at 514 nm, the SWNT-adsorbed RhB molecules were switched to a non-fluorescent form, which looked like ordinary bleaching behavior. However, after staying without light for several hours the non-fluorescent dye species turned back to the original fluorescent form. This on/off switching can be considered as a reversible photobleaching process of the dye molecules. Other irreversible photochemical pathways of RhB were strongly prohibited due to the presence of SWNTs, providing the dye molecules with a high resistance against permanent photodegradation. By determining the maximum number of reconvertable RhB molecules per unit length of the nanotubes, we have further proved that this effect only works for the first layer of adsorbed dye molecules on the SWNT surfaces.     

Constructing recyclable photocatalytic BiOBr/Ag nanowires/cotton fabric for efficient dye degradation under visible light

In this study, a highly-efficient photocatalytic and recyclable BiOBr/Ag nanowires (AgNW)/cotton fabric (CF) composite was fabricated by successive ionic layer adsorption and reaction (SILAR) for rapid treatment of dye wastewater. The integration of AgNW and BiOBr aims to establish a channel for faster and easier charge transfer to enhance the photocatalytic performance. The chemical structure and morphology of BiOBr/AgNW/CF, as well as its photo-degradation of Rhodamine B (RhB) under visible light radiation were explored. Results reveal that BiOBr/AgNW/CF exhibits remarkably enhanced photocatalytic activity over BiOBr/CF, which degrades 97 % of RhB within 90 min. BiOBr/AgNW/CF still maintains 88 % of photocatalytic degradation capacity after five reusing cycles due to the effective encapsulation of BiOBr that protects AgNW from oxidation. Photoluminescence, electron spin resonance, and free radical trapping experiments confirm that the separation efficiency of photo-generated electron-hole pairs plays an important role in improving photocatalytic performance. In all, this work exhibits great potential in the development of textile-based photocatalytic materials that integrates two significant merits, the high degradation efficiency and easy recovery.     

Composition dependence of the photocatalytic activities of BiOCl(1-x)Br(x) solid solutions under visible light

We prepared BiOCl(1-x)Br(x) (x=0-1) solid solutions and characterized their structures, morphologies, and photocatalytic properties by X-ray diffraction, diffuse reflectance spectroscopy, scanning electron microscopy, Raman spectroscopy, photocurrent and photocatalytic activity measurements and also by density functional theory calculations for BiOCl, BiOBr, BiOCl(0.5)Br(0.5). Under visible-light irradiation BiOCl(1-x)Br(x) exhibits a stronger photocatalytic activity than do BiOCl and BiOBr, with the activity reaching the maximum at x=0.5 and decreasing gradually as x is increased toward 1 or decreased toward 0. This trend is closely mimicked by the photogenerated current of BiOCl(1-x)Br(x) , indicating that the enhanced photocatalytic activity of BiOCl(1-x)Br(x) with respect to those of BiOCl and BiOBr originates from the trapping of photogenerated carriers. Our electronic structure calculations for BiOCl(0.5)Br(0.5) with the anion (O(2-), Cl(-), Br(-)) and cation (Bi(3+)) vacancies suggest that the trapping of photogenerated carriers is caused most likely by Bi(3+) cation vacancies, which generate hole states above the conduction band maximum.     

The Role of the Relative Dye/Photocatalyst Concentration in TiO2 Assisted Photodegradation Process

Despite photocatalytic degradation is studied generally focusing the catalyst, its interaction with the contaminant molecule plays a fundamental role in the efficiency of that process. Then, we proposed a comparative study about the photodegradation of two well‐known dyes, with different acidity/basicity – Methylene Blue (MB) and Rhodamine B (RhB), catalyzed by TiO₂ nanoparticles, varying both dye and photocatalyst concentrations. The results showed that the amphoteric character of MB molecules, even in a range of concentration of 5.0–10.0 mg L^?1, did not imply in pH variation in solution. Therefore, it did not affect the colloidal behavior of TiO₂ nanoparticles, independent of the relative dye/catalyst concentration. The acid–base character of RhB influenced the resultant pH of the solution, implicating in different colloidal behavior of the nanoparticles and consequently, in different degradation conditions according to dye concentration. As the isoelectric point of TiO₂ is between the pH range of the RhB solutions used in this study, from 1.0 to 7.5 mg L^?1, the resultant pH was the key factor for degradation conditions, from a well dispersed to an agglomerated suspension.     

Novel Bi/BiOBr/AgBr composite microspheres: Ion exchange synthesis and photocatalytic performance

Novel Bi/BiOBr/AgBr composite microspheres were prepared by a rational in situ ion exchange reaction between Bi/BiOBr microspheres and AgNO₃. The characteristic of the as-obtained ternary microspheres was tested by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDS), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and photoluminescence (PL). Under visible light irradiation, Bi/BiOBr/AgBr microspheres exhibited an excellent photocatalytic efficiency for rhodamine B (RhB) degradation, which was about 1.4 and 4.9 times as high as that of Bi/BiOBr and BiOBr/AgBr, demonstrating that the highest separation efficiency of charge carriers in the heterostructured Bi/BiOBr/AgBr. The photocatalytic activity of Bi/BiOBr/AgBr microspheres just exhibited a slight decrease after three consecutive cycles. The photocatalytic mechanism investigation confirmed that the superoxide radicals (O₂^•−) were the dominant reactive oxygen species for RhB degradation in Bi/BiOBr/AgBr suspension.     

Enhanced photocatalytic activity and stability of AgBr/BiOBr/graphene heterojunction for phenol degradation under visible light

In this work, we have reported synthesis of AgBr/BiOBr photocatalyst supported on graphene (Gr) using facile precipitation method. AgBr/BiOBr/Gr was characterized using various spectral techniques like FESEM, TEM, XRD, FTIR, XPS, Raman and PL analyses. AgBr/BiOBr/Gr had improved visible light absorption. PL studies indicated the reduction in recombination of photogenerated electron hole pair of AGBr/BiOBr/Gr. AFM analysis confirmed the thickness of AGBr/BiOBr/Gr was less than 8.0 nm. The higher dispersibility of photocatalyst was ascertained by Tyndall effect. AgBr/BiOBr/Gr photocatalyst was effectively used for the photodegradation of phenol from simulated water. The phenol degradation process was remarkably influenced by adsorption process. The concurrent adsorption and photocatalytic was effective for degradation of phenol. The phenol was completely mineralized into CO₂ and H₂O in 6 h. The degradation process followed pseudo first order kinetics. The results confirmed that integration of AgBr/BiOBr with graphene caused an increase in photocatalytic activity due to reduced recombination of photogenerated electron hole pair and electron sink behavior of graphene for photogenerated electrons of BiOBr. AgBr/BiOBr/Gr photocatalyst displayed significant stability and recyclability for ten catalytic cycles.     

Hierarchical porous cellulose/activated carbon composite monolith for efficient adsorption of dyes

Cheap and efficient adsorbents to remove contaminants of toxic dye molecules from wastewater are strongly in demand for environmental reasons. This study provides a novel design of a monolithic adsorbent from abundant materials via a facile synthetic procedure, which can greatly reduce the problems of the tedious separation of adsorbents from treated wastes. A hierarchically porous cellulose/activated carbon (cellulose/AC) composite monolith was prepared by thermally-induced phase separation of cellulose acetate in the presence of AC, using a mixture of DMF and 1-hexanol, followed by alkaline hydrolysis. The composite monolith had alarge specific surface area with mesopore distribution. It not only showed high uptake capacity towards methylene blue (MB) or rhodamine B (RhB) but could also simultaneously adsorb MB and RhB from their mixture, in which the adsorption of one dye was not influenced by the other one. Remarkable effects of solution pH, initial concentration of dye (C ₀), contact time, adsorbent dosage and temperature on the adsorption of MB and RhB onto the composite monolith were demonstrated. The binding data for MB and RhB adsorption on the composite monolith fitted the Freundlich model well, suggesting a heterogeneous surface of the composite monolith. The monolith could retain around 90% of its adsorption capacity after 8 times reuse. These data demonstrate that the cellulose/AC composite monolith has a large potential as a promising adsorbent of low cost and convenient separation for dye in wastewater.     

ZnS光催化剂对不同偶氮类染料光降解的光催化性能的比较

在表面活性剂十六烷基三甲基溴化铵(CTAB)存在时,合成了ZnS光催化剂。 采用X射线衍射和透射电子显微镜等测试技术结果表明,制得的ZnS粒子尺寸均一,无团聚现象,平均粒径约为3.5 nm。 研究了ZnS光催化剂在紫外光下对不同染料的光催化降解效率,结果表明,ZnS光催化剂对一些含-N=N-基团的偶氮类染料,如甲基橙(MO)、酸性嫩黄(AY)、酸性橙Ⅱ(AOⅡ)光催化降解效率高达88％以上,甲基红(MR)的光催化降解效率也达59.63%。 表明-N=N-基团容易降解。 染料分子本身的吸光性也起一定的作用,虽然二甲酚橙(XO)和亚甲基蓝(MB)分子中均不含-N=N-基团,但由于XO的最大吸收峰分布于430 nm的紫外光区,其光催化降解效率可达43.83％,而MB最大吸收峰分布于664 nm可见光区,因此,其光催化降解效率则非常低。     

One‐Pot Synthesis,Characterization, and Enhanced Photocatalytic Activity of a BiOBr–Graphene Composite

Herein, a chemically bonded BiOBr–graphene composite (BiOBr–RG) was prepared through a facile in situ solvothermal method in the presence of graphene oxide. Graphene oxide could be easily reduced to graphene under solvothermal conditions, and simultaneously BiOBr nanoplates with pure tetragonal phase were grown uniformly on the graphene surface. The structure and photoelectrochemical properties of the resulting materials were characterized by transmission electron microscopy (TEM), X‐ray diffraction (XRD), Fourier‐transform infrared (FTIR) spectroscopy, Raman spectroscopy, X‐ray photoelectron spectroscopy (XPS), and impedance and photocurrent action measurements. The combination of BiOBr and graphene introduces some properties of graphene into the photocatalysis reaction, such as excellent conductivity, adsorptivity, and controllability. A remarkable threefold enhancement in the degradation of rhodamine B (RhB) was observed with as‐prepared BiOBr–RG as compared with pure BiOBr under visible light (λ>420 nm). The enhanced photocatalytic activity could be attributed to the great adsorptivity of dyes, the extended photoresponse range, the negative shift in the Fermi level of BiOBr–RG, and the high migration efficiency of photoinduced electrons, which may effectively suppress the charge recombination.     

New photocatalyst BiOCl/BiOI composites with highly enhanced visible light photocatalytic performances

BiOCl/BiOI composites with a visible light response were prepared by a simple hydrothermal method. Even though both single BiOCl and BiOI show low photocatalytic activity, BiOCl/BiOI composites provide enhanced efficiency in decomposing organic compounds including Methyl Orange (MO) and Rhodamine B (RhB). Furthermore, the 20%BiOCl/BiOI composite shows the highest efficiency for decomposing MO, while the highest performance is observed for the degradation of RhB over 70%BiOCl/BiOI composite. A possible photocatalytic mechanism has been proposed based on the relative experiments and the band positions of BiOCl and BiOI.     

g-C_3N_4/BiOBr异质结光催化剂的制备与可见光催化活性

以三聚氰胺作为合成g-C_3N_4纳米片的前躯体,以Bi(NO3)3·5H2O和KBr作为合成BiOBr的原料,采用水热法构建g-C_3N_4/Bi OBr二维异质结可见光催化剂,有效的晶面复合和合适的能带组合有助于增强g-C_3N_4和BiOBr的可见光催化活性。利用X射线衍射(XRD)、透射电镜(TEM)、X射线光电子能谱(XPS)、光致发光光谱(PL)和紫外-可见漫反射光谱(UVvis DRS)等方法表征其结构、光学性质以及组成结构。在可见光(λ420 nm)下以光催化降解RhB来评价合成催化剂的光催化活性,结果表明,g-C_3N_4/BiOBr光催化降解罗丹明B(Rh B)的效率高于单体g-C_3N_4和BiOBr,并对g-C_3N_4/BiOBr增强可见光催化RhB机理进行解释。