Synergetic effect of ZnIn2S4 nanosheets with metal-organic framework molding heterostructure for efficient visible- light driven photocatalytic reduction of Cr(VI)

The photocatalytic reduction of toxic Cr(VI), to green Cr(III) by visible light, is highly required. Metal-organic frameworks have been waged more and more devotion in the field of environmental remediation. Diversification along with functionalization is still thought-provoking and crucial for the progress of metal-organic framework (MOF)-based high activity materials. Herein, a succession of UiO-66-NH₂@ZnIn₂S₄ composites with varying amount of UiO-66-NH₂ is prepared by the facile solvothermal technique. Synergetic effect for Cr(VI) reduction is assessed under the influence of visible light (λ > 420 nm). UiO-66-NH₂ octahedron is detained by ZnIn₂S₄ nanoflakes. The obvious enhancement in activity is observed which is credited to the well-suited energy band construction and close interaction between the interface of ZnIn₂S₄ and UiO-66-NH₂, which leads to effective transfer and separation of photogenerated carriers. Synergistic effect could be evidently understood from the PL and UV -spectroscopy, after molding into heterostructure of UiO-66-NH₂@ZnIn₂S₄. In addition, UiO-66-NH₂@ZnIn₂S₄ composites exhibited good stability in photocatalytic reduction. Consequently, this UiO-66-NH₂ constructed composite has high potential in the field of environmental remediation.     

Synergistic improvement of Cr(VI) reduction and RhB degradation using RP/g-C3N4 photocatalyst under visible light irradiation

The RP/g-C₃N₄ heterojunction photocatalyst was fabricated by a facile heat treatment strategy. The obtained composite has excellent light harvesting ability and charge separation performance. Compared to single RP and g-C₃N₄, the 50%-RP/g-C₃N₄ exhibited enhanced photocatalytic activity for simultaneously removing Cr(VI) and RhB, and the removal rates can reach 92% and 99% in 25 min, respectively. The enhanced mechanism was revealed by active species capturing experiments, showing that electrons can reduce Cr(VI) and produce O₂^– in air and that holes can directly oxidize the dyes. The coexistence of Cr(VI) and RhB will lead to a synergistic improvement of Cr(VI) reduction and RhB degradation due to rapid surface reactions. This further improves the charge separation except for the heterojunction effect. In addition, the COD analysis demonstrates that organic dyes are mainly degraded into CO₂, H₂O and some intermediates.     

Enhanced photocatalytic Cr(VI) reduction and diclofenac sodium degradation under simulated sunlight irradiation over MIL-100(Fe)/g-C3N4 heterojunctions

Metal-organic framework MIL-100(Fe) and g-C₃N₄ heterojunctions (MG-x, x = 5%, 10%, 20%, and 30%, x is the mass fraction of MIL-100(Fe) in the hybrids) were facilely fabricated through ball-milling and annealing, and characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, transmission electron microscopy, UV-visible diffuse-reflectance spectrometry, and photoluminescence emission spectrometry. The photocatalytic activities of the series of MG-x heterojunctions toward Cr(VI) reduction and diclofenac sodium degradation were tested upon irradiation with simulated sunlight. The influence of different organic compounds (ethanol, citric acid, oxalic acid, and diclofenac sodium) as hole scavengers and the pH values (2, 3, 4, 6, and 8) on the photocatalytic activities of the series of MG-x heterojunctions was investigated. MG-20% showed superior photocatalytic Cr(VI) reduction and diclofenac sodium degradation performance than did the individual MIL-100(Fe) and g-C₃N₄ because of the improved separation of photoinduced electron-hole charges, which was clarified via photoluminescence emission and electrochemical data. Moreover, the MG-x exhibited good reusability and stability after several runs.     

Photocatalytic Reduction of Cr (VI) over g-C3N4 Photocatalysts Synthesized by Different Precursors

Graphitic carbon nitride (g-C₃N₄) photocatalysts were synthesized via a one-step pyrolysis process using melamine, dicyandiamide, thiourea, and urea as precursors. The obtained g-C₃N₄ materials exhibited a significantly different performance for the photocatalytic reduction of Cr(VI) under white light irradiation, which is attributed to the altered structure and occupancies surface groups. The urea-derived g-C₃N₄ with nanosheet morphology, large specific surface area, and high occupancies of surface amine groups exhibited superior photocatalytic activity. The nanosheet morphology and large surface area facilitated the separation and transmission of charge, while the high occupancies of surface amine groups promoted the formation of hydrogen adsorption atomic centers which were beneficial to Cr(VI) reduction. Moreover, the possible reduction pathway of Cr(VI) to Cr(III) over the urea-derived g-C₃N₄ was proposed and the reduction process was mainly initiated by a direct reduction of photogenerated electrons.     

Facile synthesis of GO as middle carrier modified flower-like BiOBr and C3N4 nanosheets for simultaneous treatment of chromium(VI) and tetracycline

A novel GO modified g-C₃N₄ nanosheets/flower-like BiOBr hybrid photocatalyst is fabricated by a facile method. The characterization results reveal that wrinkled GO is deposited between g-C₃N₄ nanosheets and flower-like BiOBr forming a Z-scheme heterojunction. As a mediator, plicate GO plays a positive role in prompting photogenerated electrons transferring through its sizeable 2D/2D contact surface area. The g-C₃N₄/GO/BiOBr hybrid displays a superior photocatalytic ability to g-C₃N₄ and BiOBr in photodegrading tetracycline (TC), whose removal efficiency could reach 96% within 2 h. Besides, g-C₃N₄/GO/BiOBr composite can reduce Cr(VI), and simultaneously treat TC and Cr(VI) combination contaminant under the visible light. The g-C₃N₄/GO/BiOBr ternary composite also exhibits satisfactory stability and reusability after four cycling experiments. Further, a feasible mechanism related to the photocatalytic process of g-C₃N₄/GO/BiOBr is put forward. This study offers a ternary hybrid photocatalyst with eco-friendliness and hopeful application in water pollution.     

Bifunctional TiO2 Catalysts for Efficient Cr(VI) Photoreduction Under Solar Light Irradiation Without Addition of Acids

Bifunctional TiO₂ photocatalysts co-doped with nitrogen and sulfur were prepared by the controlled thermal decomposition of ammonium titanyl sulfate precursor. They have both photocatalytic activity and Br?nsted acidity, and thus are active in the photoreduction of Cr(VI) under solar light irradiation without the addition of acids. The activity is superior to that of Degussa P25 in the acidified suspension at the same pH adjusted by H₂SO₄.     

Photocatalytic Cr(VI) sequestration and photo-Fenton bisphenol A decomposition over white light responsive PANI/MIL-88A(Fe)

Polyaniline (PANI)/MIL-88A(Fe) (Px@M88) composites were constructed through a simple one-pot hydrothermal method. The photocatalytic and photo-Fenton activities of Px@M88 composites toward reduction of Cr(VI) and degradation organic pollutants were explored by white light irradiation. PANI, as a conductive polymer, can improve MIL-88A(Fe)’s conductivity and the efficiency of photogenerated e⁻–h⁺ pair separation. In the presence of H₂O₂, a photo-Fenton reaction occured to boost the degradation efficiency of organic pollutants like bisphenol A. In addition, P9@M88 showed excellent recycling and stability in cycling experiments. Finally, a possible reaction mechanism for photocatalytic degradation was proposed and verified by X-ray photoelectron spectroscopy and electron spin resonance determination and electrochemical characterizations.     

ZnO–Bentonite nanocomposite: an efficient catalyst for discharge of dyes,phenol and Cr(VI) from water

The present work focused on application of ZnO-NPs@bentonite, as a catalyst, for disposal of different pollutants such as dyes, phenol compounds and Cr(VI) ions from water. The prepared ZnO–bentonite nanocomposite was characterized by using FT-IR, X-ray powder diffraction, and Scanning electron microscopy analysis. The results showed that the amount of zinc oxide influenced the catalytic performance of ZnO–bentonite nanocomposite. Small amounts of zinc oxide on bentonite have a positive effect whereas increase in weight ratios has a negative effect.

     

TiO2/EDTA-rich carbon composites: Synthesis,characterization and visible-light-driven photocatalytic reduction of Cr(VI)

TiO₂/EDTA-rich carbon composites exhibits excellent photoreduction of Cr(VI) activity via ligand-to-metal charge transfer process.     

Study of the complexation and precipitation equilibria in the system Cr(VI)-Fe(III)-H2O

Potentiometric and spectrophotometric studies of the systems Cr(VI)-Fe(III)-H₂O and Fe(III)-H₂O systems have been performed. The formation of the complex FeCrO ₄ ⁺ is suggested and the corresponding thermodynamic formation constant has been calculated (log₁₁ = 7.77 ± 0.02) . In order to understand the cation-anion interactions, a study of the precipitation equilibrium between Cr(VI) and Fe(III) has been carried out. The results indicate the formation of FeOHCrO₄·2Fe(OH)₃, a mixed precipitate whose thermodynamic solubility product is pK_so=99.8±0.2.     

Ag/NH2-MIL-125(Ti)的构建及可见光还原水中Cr(Ⅵ)

开发高效、稳定的复合光催化材料是当前环境领域的迫切需求。 本文采用溶剂热协同紫外光还原法成功制备了复合光催化材料Ag/NH₂-MIL-125(Ti),并通过X射线衍射(XRD)、扫描电子显微镜(SEM)、能谱(EDS)、紫外-可见漫反射光谱(UV-Vis DRS)及X射线光电子能谱(XPS)等技术手段对其形貌、结构及光学性质进行分析,考察了Ag/NH₂-MIL-125(Ti)可见光(λ≥420 nm)催化还原Cr(Ⅵ)的性能,并优化了催化剂用量、Cr(Ⅵ)浓度、空穴捕捉剂种类及用量等条件。 结果表明,在最佳条件下,Ag/NH₂-MIL-125(Ti)具有良好的吸附及光催化还原Cr(Ⅵ)性能,其吸附及光催化还原率是NH₂-MIL-125(Ti)的3.11倍,Ag/NH₂-MIL-125(Ti)特殊的“芝麻饼”形貌以及Ag⁰与NH₂-MIL-125(Ti)之间形成的异质结有助于增强复合材料的光催化还原Cr(Ⅵ)的性能。 同时,通过条件实验,提出了光催化还原过程中主要的活性物种以及Cr(Ⅵ) 的还原机理。 本研究将为金属有机骨架(MOFs)复合材料在可见光催化环境修复领域的应用提供理论依据和实验参考。     

Highly efficient removal of Cr(VI) from wastewater via adsorption with novel magnetic Fe3O4@C@MgAl-layered double-hydroxide

Novel magnetic Fe₃O₄@C@MgAl-layered double-hydroxide (LDH) nanoparticles have been successfully prepared by the chemical self-assembly methods. The properties of surface functional groups, crystal structure, magnetism and surface morphology of magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), thermal gravity-differential thermal gravity (TG-DTG), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The adsorption studies of the novel adsorbent in removing heavy metals Cr (VI) from waste water showed that the maximum absorption amount of Cr(VI) was 152.0 mg/g at 40℃ and pH 6.0. The excellent adsorption capacity of the Fe₃O₄@C@MgAl-LDH nano-absorbents plus their easy separation, environmentally friendly composition and reusability makes them more suitable adsorbents for the removal of metal ions from waste water.     

氨基功能化纳米Fe3O4磁性高分子吸附剂对废水中Cr(VI)的吸附研究

采用分散聚合法通过共聚、开环反应, 对纳米Fe3O4进行表面功能化修饰, 得到富含NH2官能团的纳米磁性高分子复合材料. 通过透射电镜(TEM)、振动样品磁强计(VSM)、热重差热分析(TGA)、X射线衍射(XRD)、红外光谱(IR)等对其进行表征, 着重研究了其作为吸附剂对Cr(VI)的吸附性能. 结果表明: 该吸附剂对Cr(VI)的吸附能在10 min内达到平衡; 废水溶液pH值能显著影响吸附剂对Cr(VI)的吸附效果, pH为2.5时效果最佳. 废水中Cr(VI)的初始浓度、吸附时间、温度等因素对吸附效果均有不同程度的影响. 结合相应pH值下Cr(VI)的形态分布, 探讨了这种新型材料对Cr(VI)的吸附机理. 结果表明: 其吸附机理及吸附容量与废水中Cr(VI)的离子形式有关; 吸附过程以离子交换与静电引力为主. 等温吸附数据符合Langmuir模型, T＝308 K, pH＝2.5, V＝40 mL时, 吸附剂的饱和吸附容量qm＝25.58 mg/g. 吸附为吸热过程, 焓变ΔH＝8.64 kJ/mol.     

微流控法制备的多孔微球对Cr(Ⅵ)的吸附性能

利用玻璃毛细管搭建单级微流控装置制备单分散水包油（O/W）乳液,以乳液为模板,紫外光照射乳液引发自由基聚合,成功制备了单分散甲基丙烯酸甲酯/甲基丙烯酸二甲基氨基乙酯（MMA/DMAEMA）多孔微球。微球粒径偏差系数（CV）值小于5%,单分散性良好。研究了MMA/DMAEMA多孔微球对Cr(Ⅵ)的吸附性能、再生吸附性能、吸附机理。结果表明：pH对微球吸附Cr(Ⅵ)的量有较大影响,当pH=3时,微球对Cr(Ⅵ)吸附率达到52.9%;循环4次后微球吸附率基本不降低,循环性能好;微球吸附符合准二级动力学模型,属于化学吸附;微球等温吸附符合Langmuir模型,属于单分子层吸附。     

N-Doped Carbon Coated TiC Nanofiber Arrays on Ti-6Al-4V for Sensitive Electrochemical Determination of Cr(VI)

A sensitive electrochemical sensor for Cr(VI) detection based on N-doped carbon coated TiC nanofiber arrays (TiC@CNx NFAs) is reported. The abundant electrocatalytic active sites contained CNx shell, highly conducting TiC core, and good electrical contact between the TiC@CNx and underlying Ti alloy endow this electrode with the excellent electrochemical sensing properties. The developed electrochemical sensor shows remarkable determination activity towards Cr(VI) with a high sensitivity of 0.88 μA μM⁻¹ cm⁻², a low detection limit of 4.0 nM (S/N=3), a wide linear range from 0.2 to 24.1 μM, good selectivity and anti-interference property.     

A Cd(II) Luminescent Coordination Grid as a Multiresponsive Fluorescence Sensor for Cr(VI) Oxyanions and Cr(III), Fe(III), and Al(III) in Aqueous Medium

Hydro(solvo)thermal reactions of Cd(NO₃)₂, N-(pyridin-3-ylmethyl)-4-(pyridin-4-yl)-1,8-naphthalimide (NI-mbpy-34), and 5-bromobenzene-1,3-dicarboxylic acid (Br-1,3-H₂bdc) afforded a luminescent coordination polymer, {[Cd(Br-1,3-bdc)(NI-mbpy-34)(H₂O)]∙2H₂O}_n (1). Single-crystal X-ray diffraction analysis showed that 1 features a two-dimensional (2-D) gridlike sql layer with the point symbol of (4⁴·6²), where the Cd(II) center adopts a {CdO₅N₂} pentagonal bipyramidal geometry. Thermogravimetric (TG) analysis confirmed the thermal stability of 1 up to about 340 °C, whereas XRPD patterns proved the maintenance of crystallinity and framework integrity of 1 in CH₂Cl₂, H₂O, CH₃OH, and toluene. Photoluminescence studies indicated that 1 displayed intense blue fluorescence emissions in both solid-state and H₂O suspension-phase. Owing to the good fluorescent properties, 1 could serve as an excellent turn-off fluorescence sensor for selective and sensitive Cr(VI) detection in water, with LOD = 15.15 μM for CrO₄²⁻ and 14.91 μM for Cr₂O₇²⁻, through energy competition absorption mechanism. In addition, 1 could also sensitively detect Cr³⁺, Fe³⁺, and Al³⁺ ions in aqueous medium via fluorescence-enhancement responses, with LOD = 2.81 μM for Cr³⁺, 3.82 μM for Fe³⁺, and 3.37 μM for Al³⁺, mainly through an absorbance-caused enhancement (ACE) mechanism.     

Study of the complexation and precipitation equilibria in the system Cr(VI)-Cu(II)-H2O

A potentiometric and spectrophotometric study of the system Cr(VI)–Cu(II)–H₂O has been performed. The formation of the complex CuCrO₄ is suggested and the corresponding thermodynamic formation constant has been calculated (log ₁₁ ⁰ = 3.27 ± 0.11). The study of the precipitation equilibrium between Cr(VI) and Cu(II) has also been carried out. The results indicate the formation of a mixed precipitate with formula CuCrO₄·2Cu(OH)₂ whose corresponding thermodynamic solubility product is p K _so ^o =48.6±0.2.     

In-situ construction of amorphous/crystalline contact Bi2S3/Bi4O7 heterostructures for enhanced visible-light photocatalysis

Constructing a heterojunction photocatalyst is a significant method to enhance photocatalytic activity because it can promote the separation of photogenerated carriers. Herein, amorphous/crystalline contact Bi₂S₃/Bi₄O₇ heterostructure was successfully synthesized by in-situ sulfidation of Bi₄O₇. The amorphous Bi₂S₃ is diffused on the surface of Bi₄O₇ rod, enhancing the visible light response and improving the transport of photogenerated carriers. Various characterizations confirm that the rapid separation of photogenerated carriers leads to increased photocatalytic performance. The optimized Bi₂S₃/Bi₄O₇ heterostructure photocatalyst (BiS-0.15) exhibits the highest Cr(VI) reduction (0.01350 min⁻¹) and RhB oxidation (0.08011 min⁻¹) activity, which is much higher than that of pure Bi₄O₇ and Bi₂S₃/Bi₄O₇ mixture under visible light irradiation. This work provides new insights into the construction of efficient novel photocatalysts.     

Determination of pKa value, kinetic studies of decomposition and oxygen transfer for chromium(VI) peroxide

The determination of pK_a value for the unstable chromium(VI) peroxide, CrO(O₂)₂(H₂O) in aqueous solution is presented. The pK_a value is found to be (1.55 ± 0.03). The kinetic decomposition of chromium(VI) peroxide is dependent on the concentration of hydrogen peroxide in the pH range between 2.5 and 4.0. We have proposed the possible explanation for the formation of triperoxo chromium complex of hydrogen peroxide which is dependent on decomposition. Activation of coordinate peroxide in chromium(VI) peroxide observed in the kinetic studies is by reduction of thiolato-cobalt(III) complex. The rate constant (M⁻¹ s⁻¹, 15 °C) for the oxygen atom transfer reaction from CrO(O₂)₂(OH)⁻ to (en)₂Co(SCH₂CH₂NH₂)²⁺ is found to be (25.0 ± 1.3).