Decolorization and mineralization of textile dyes at solution bulk by heterogeneous nanophotocatalysis using immobilized nanoparticles of titanium dioxide

Nanophotocatalysis using nanostructured semiconductors constitute one of the emerging technologies for destructive oxidation of organics such as dyes. This paper deals with the decolorization and mineralization of reactive dyes by heterogeneous nanophotocatalysis using an immobilized TiO₂ nanoparticle photocatalytic reactor. A simple and effective method was used to immobilization of titanium dioxide nanoparticles. Reactive Orange 107 (RO 107, sulphatoethylsulphonyl reactive dye) and Reactive Red 152 (RR 152, monochlorotriazine reactive dye) were used as model compounds. UV–vis and ion chromatography (IC) analyses were employed to obtain the details of the photocatalytic degradation of the selected dyes. The effects of operational parameters such as H₂O₂, dye concentration, anions (NO₃⁻, Cl⁻, SO₄²⁻, HCO₃⁻ and CO₃²⁻) and pH were investigated. Formate, acetate and oxalate anions were detected as dominant aliphatic intermediates where, they were further oxidized slowly to CO₂. Nitrate, sulfate and chloride anions were detected as the photocatalytic mineralization of RO 107 and RR 152. Kinetics analysis indicates that the photocatalytic decolorization rates can usually be approximated zero-order model for RO 107 and first-order model for RR 152 dyes. Results show that the photocatalytic process occurred at solution bulk and the employment of optimal operational parameters may lead to complete decolorization and mineralization of dye solutions.     

Mechanism of TiO2-assisted photocatalytic degradation of dyes under visible irradiation: photoelectrocatalytic study by TiO2-film electrodes

Photoelectrocatalytic degradation of various dyes under visible light irradiation with a TiO(2) nanoparticles electrode has been investigated to reveal the mechanism for TiO(2)-assisted photocatalytic degradation of dyes. The degradation of both cationic and anionic dyes at different biases, including the change in the degradation rate of the dyes and the photocurrent change with the bias potential, the degraded intermediates, the voltage-induced adsorption of dyes, the accumulation of electrons in the TiO(2) electrode, the effect of various additives such as benzoquinone (BQ) and N,N-dimethyl aniline (DMA), and the formation of active oxygen species such as O(2)(*-) and H(2)O(2) were examined by UV-visible spectroscopy, HPLC, TOC, and spin-trap ESR spectrometry. It was found that the dyes could controllably interact with the TiO(2) surface by external bias changes and charging of dyes. The cationic dyes such as RhB and MG underwent efficient mineralization at negative bias, but the N-dealkylation process predominated at positive bias under visible light irradiation. The discolorations of the anionic dyes SRB and AR could not be accelerated significantly at either negative or positive bias. At a negative bias of -0.6 V vs SCE, O(2)(*-) and dye(*+) were formed simultaneously at the electrode/electrolyte interface during degradation of cationic RhB. In the case of anionic dyes, however, it is impossible for the O(2)(*-) and dye cationic radical to coexist at the electrode/electrolyte surface. Experimental results imply both the superoxide anionic radical and the dye cationic radical are essential to the mineralization of the dyes under visible light-induced photocatalytic conditions.     

Photocatalytic Degradation of Organic Reactive Dyes over MnTiO3/TiO2 Heterojunction Composites Under UV‐Visible Irradiation

In this study, the photocatalytic degradation of organic reactive dyes have been investigated using MnTiO₃/TiO₂ heterojunction composites in the presence of electron acceptors under UV‐Visible light irradiation. This MnTiO₃/TiO₂ heterojunction composites were prepared by annealing different mass ratios of pyrophanite MnTiO₃ (3–11 wt%) and TiO₂ at 300°C. All the MnTiO₃/TiO₂ heterojunction composites were characterized by spectral techniques like X‐ray diffraction (XRD), scanning electron microscope (SEM) and diffused reflectance UV‐visible spectroscopic analysis (DRS). Among them, 9 wt% MnTiO₃/TiO₂ heterojunction composites exhibited higher photocatalytic activity for the degradation of Reactive Blue 4 (RB 4). The photocatalytic efficiency of 9 wt% MnTiO₃/TiO₂ heterojunction composites was further enhanced by the addition of substantial amount of electron acceptors like hydrogen peroxide (H₂O₂) and ammonium peroxydisulfate ([NH₄]₂S₂O₈). The presence of oxidants (electron acceptors) facilitates the fast degradation of dye solution even in higher concentration upto 200 mg/L. The photocatalytic activity of MnTiO₃/TiO₂ heterojunction composites was also studied for the degradation of other four different structured reactive dyes. The extent of mineralization of these organic reactive dyes during photocatalytic degradation was estimated from COD analysis. MnTiO₃/TiO₂ heterojunction composites was also found to have good photostability in the presence of oxidants.     

Single-molecule fluorescence imaging of the remote TiO2 photocatalytic oxidation

The remote TiO2 photocatalytic oxidation reaction of single dyes has been investigated by the single-molecule fluorescent imaging technique. The present results suggest that the active oxygen species (Ox) is most probably the .OH radical, which is generated from the photodecomposition of H2O2 by UV light. The analyses of the number, intensity, and spectrum of individual fluorescence spots at the single-molecule level also indicate that unoxidized and oxidized dyes exist during the bleaching processes of single dyes.     

The effect of recycling flux on the performance and microbial community composition of a biofilm hydrolytic-aerobic recycling process treating anthraquinone reactive dyes

Synthetic dyes are extensively used and rarely degraded. Microbial decomposition is a cost-effective alternative to chemical and physical degradation processes. In this study, the decomposition of simulated anthraquinone reactive dye (Reactive Blue 19; RB19) at a concentration of 400-mg/L in wastewater by a biofilm hydrolytic-aerobic recycling system was investigated over a range of recycling fluxes. The 16S rDNA-based fingerprint technique was also used to investigate the microbial community composition. Results indicated that the recycling flux was a key factor that influenced RB19 degradation. The RB19 and COD removal efficiency could reach values as high as 82.1% and 95.4%, respectively, with a recycling flux of 10 mL/min. Molecular analysis indicated that some strains were similar to Aeromonadales, Tolumonas, and some uncultured clones were assumed to be potential decolorization bacteria. However, the microbial community composition in the reactors remained relatively stable at different recycling fluxes. This study provided insights on the decolorization capability and the population dynamics during the decolorization process of anthraquinone dye wastewater.     

二氧化钛纳米管的制备与光催化活性

用阳极氧化法,室温条件下在含NH4F和H2O的电解液(丙三醇+NH4F+H2O;乙二醇+NH4F+H2O)中制备了TiO2纳米管阵列。用环境扫描电子显微镜(SEM)、X射线衍射仪(XRD)表征二氧化钛纳米管阵列的微观形貌和物相结构。在丙三醇电解液中,电压为60 V,65 V,70 V,75 V制备的纳米管直径依次为160、170、190、220 nm。对甲基橙(10 mg/L)降解测试TiO2纳米管阵列的光催化性能。研究结果表明:在100 V阳极电压制备经过500℃退火处理后的TiO2纳米管阵列的光催化效果最好,其光催化降解率在光照时间120 min时达到89.2%。     

Free and Ca-Alginate Beads Immobilized Horseradish Peroxidase for the Removal of Reactive Dyes: an Experimental and Modeling Study

The aim of this work was to remove the dyes Reactive Blue 221 (RB 221) and Reactive Blue 198 (RB 198) of synthetic effluent using the immobilized enzyme horseradish peroxidase (HRP) in Ca-alginate beads. Experimental parameters affecting the dye removal process such as the effect of pH, temperature, hydrogen peroxide concentration, mass capsules, and reuse were evaluated, and a numerical model of mass transfer was developed. A maximum removal of 93 and 75%, respectively, for the dyes RB 221 and RB 198, at pH 5.5 and temperature of 30 °C, concentration of hydrogen peroxide of 43.75 μM for dye RB 221 and 37.5 μM for the dye of RB 198 was obtained. A removal reaction of 180 min for RB 221 and 240 min for RB 198 was observed. Three reuse cycles of use of immobilized enzyme were achieved for both dyes. The numerical model proposed led to a good fit compared to experimental data. The HRP enzyme immobilized in Ca-alginate capsules showed a great potential for biotechnological applications, especially for the removal of reactive dyes.     

H2O2/TiO2超声协同光降解活性艳橙的研究

以活性艳橙溶液为模拟废水,通过H₂O₂/TiO₂超声(US)协同作用光降解活性艳橙溶液,探讨了TiO₂催化剂用量、H₂O₂用量、活性艳橙溶液的初始浓度、pH值、TiO₂催化剂锻烧温度等对活性艳橙溶液降解率的影响,并比较了几种不同作用方式对活性艳橙溶液的降解效果.结果表明:UV/H₂O₂/TiO₂/US协同作用降解活性艳橙溶液的效果最好;当活性艳橙溶液的初始浓度为20 mg·L^-1,pH＝5,TiO₂用量为0.4 g·L^-1,H₂O₂用量为0.4 ml·L^-1时,降解率可达92.06%.     

Reductive decolorization of a textile reactive dyebath under methanogenic conditions

The objective of the present study was to assess the biological decolorization of an industrial, spent reactive dyebath and its three dye components (Reactive Blue 19 [RB 19], Reactive Blue 21 [RB 21], and Reactive Red 198 [RR 198]) under methanogenic conditions. Using a mixed, methanogenic culture, batch assays were performed to evaluate the rate and exten of color removal as well as any potential toxic effects. Overall, a high rate and extent of color removal (>10 mg/[L·h] and 88%, respectively) were observed in cultures amended with either RB19 (an anthraquinone dye) or spent dyebath at an initial dye concentration of 300 mg/L (expressed as RB 19 equivalent) and 30 g/L of NaCl. Inhibition of acidogenesis and, to a larger degree, of methanogenesis resulting in accumulation of volatile fatty acids was observed in both RB 19- and spent dyebath-amended cultures. RB 21 (a phthalocyanine dye) and RR 198 (an azo dye) tested at an initial concentration of 300 mg/L did not result in any significant inhibition of the mixed methanogenic culture. Based on results obtained with cultures amended with RB 19 with and without NaCl, as well as a control culture amended with 30 g/L of NaCl, salt was less inhibitory than either RB 19 or the dyebath. Therefore, the toxic effect of the spent dyebath is at least partially attributed to its major dye component RB 19 and NaCl. Further testing of the effect of RB 19 decolorization products on the methanogenic activity in the absence of NaCl demonstrated that these products are much less inhibitory than the parent dye. Although color removal occurred despite the severe culture inhibition, biological decolorization of full-strength reactive spent dyebaths using methanogenic cultures in a repetitive, closed-loop system is not deemed feasible. For this reason, a fermentative and halotolerant culture was developed and successfully used in our laboratory for the decolorization of industrial reactive dyebaths with 100 g/L of NaCl.     

Steady-state photocatalytic epoxidation of propene by O2 over V2O5SiO2 photocatalysts

A silica-supported, lowly loaded vanadium oxide (V2O5/SiO2) photocatalyst promotes the photocatalytic epoxidation of propene with O2 at steady state in a flow reactor system. Very little deep oxidation of propene into CO2 takes place over V2O5/SiO2, in contrast to the results obtained over a TiO2 photocatalyst in which total oxidation is the main path. With each loading, the sums of the selectivities into propene oxide (PO) and propanal (PA) at steady state were almost the same. The monomeric VO4 tetrahedral species dispersed on SiO2 yield PO under UV irradiation. The less dispersed vanadium oxide species on SiO2 promote the isomerization of PO into PA. We utilized a flow reactor system in which the short contact time reduced the isomerization and resultant decomposition of PO over the catalyst surface.     

有机染料罗丹明B在复合催化剂TiO2-APS-PW11Ni作用下的光降解研究

利用自组装方式制备了多酸-有机胺-二氧化钛复合催化剂K5Ni(H2O)PW11O39-APS-TiO2(APS为(C2H5O)3SiCH2CH2CH2NH2的简称),简称为TiO2-APS-PW11Ni,通过红外(IR),紫外漫反射(UV/DRS)对其组成和结构进行了表征.并利用该催化剂光降解染料污染物罗丹明B(RB)水溶液,与纳米TiO2催化剂光降解进行对比,结果表明,染料罗丹明B在复合催化剂作用下的催化效果明显优于TiO2光催化效果,计算得降解半衰期分别为:T1/2(复合催化剂)＝6.5 min,T1/2(TiO2)＝21.2 min.     

Hydrothermal synthesis, structure and photocatalytic property of nano-TiO_2-MnO_2

TiCI4 and MnSO4.H2O as raw materials are hydrolyzed stiochiometrically, following the intermediate of oxide hydrating reacts at 150℃, 0.5 MPa in high-pressure reactor, after filtering, washing and drying, nanometric TiO2-MnO2 (Ti1-xMnxO2) is prepared. The effects of the reaction temperature and time on nanometric TiO2-MnO2 are also discussed. XRD shows that the product is TiO2-MnO2 with amorphous phase. After being sintered at above 780℃, it transfers into Ti1-xMnxO2 with a rutile structure. TEM shows that TiO2-MnO2 is the spherical particle. And the average diameter of the particles is 20 nm. The optical absorbance was determined by UV-265 spec-trophotometer after dispersing the sample in the mixture of water and glycerol with the ratio of 1 : 1 equably. It is found that the nano-material possesses the advantages of both nano-TiO2 and nano-MnO2, and it has strong absorption in the UV and visible region. Photodegradation of dyes in an aqueous solution is investigated using nanometricTiO2-MnO2 as a pho     

Preparation and enhanced visible-light photocatalytic H2-production activity of CdS-sensitized Pt/TiO2 nanosheets with exposed (001) facets

CdS-sensitized Pt/TiO(2) nanosheets with exposed (001) facets were prepared by hydrothermal treatment of a Ti(OC(4)H(9))(4)-HF-H(2)O mixed solution followed by photochemical reduction deposition of Pt nanoparticles (NPs) on TiO(2) nanosheets (TiO(2) NSs) and chemical bath deposition of CdS NPs on Pt/TiO(2) NSs, successively. The UV and visible-light driven photocatalytic activity of the as-prepared samples was evaluated by photocatalytic H(2) production from lactic acid aqueous solution under UV and visible-light (λ ≥ 420 nm) irradiation. It was shown that no photocatalytic H(2)-production activity was observed on the pure TiO(2) NSs under UV and/or visible-light irradiation. Deposition of CdS NPs on Pt/TiO(2) NSs caused significant enhancement of the UV and visible-light photocatalytic H(2)-production rates. The morphology of TiO(2) particles had also significant influence on the visible-light H(2)-production activity. Among TiO(2) NSs, P25 and the NPs studied, the CdS-sensitized Pt/TiO(2) NSs show the highest photocatalytic activity (13.9% apparent quantum efficiency obtained at 420 nm), exceeding that of CdS-sensitized Pt/P25 by 10.3% and that of Pt/NPs by 1.21%, which can be attributed to the combined effect of several factors including the presence of exposed (001) facets, surface fluorination and high specific surface area. After many replication experiments of the photocatalytic hydrogen production in the presence of lactic acid, the CdS-sensitized Pt/TiO(2) NSs did not show great loss in the photocatalytic activity, confirming that the CdS/Pt/TiO(2) NSs system is stable and not photocorroded.     

Synthesis, property characterization and photocatalytic activity of the novel composite polymer polyaniline/Bi2SnTiO7

A novel polyaniline/Bi(2)SnTiO(7 )composite polymer was synthesized by chemical oxidation in-situ polymerization method and sol-gel method for the first time. The structural properties of novel polyaniline/Bi(2)SnTiO(7) have been characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray spectrometry. The lattice parameter of Bi(2)SnTiO(7) was found to be a = 10.52582(8) ?. The photocatalytic degradation of methylene blue was realized under visible light irradiation with the novel polyaniline/Bi(2)SnTiO(7) as catalyst. The results showed that novel polyaniline/Bi(2)SnTiO(7 )possessed higher catalytic activity compared with Bi(2)InTaO(7) or pure TiO(2) or N-doped TiO(2) for photocatalytic degradation of methylene blue under visible light irradiation. The photocatalytic degradation of methylene blue with the novel polyaniline/Bi(2)SnTiO(7) or N-doped TiO(2) as catalyst followed first-order reaction kinetics, and the first-order rate constant was 0.01504 or 0.00333 min(-1). After visible light irradiation for 220 minutes with novel polyaniline/Bi(2)SnTiO(7 )as catalyst, complete removal and mineralization of methylene blue was observed. The reduction of the total organic carbon, the formation of inorganic products, SO(4)2- and NO(3-), and the evolution of CO(2) revealed the continuous mineralization of methylene blue during the photocatalytic process. The possible photocatalytic degradation pathway of methylene blue was obtained under visible light irradiation.     

Structural characterization of reactive dyes using liquid secondary ion mass spectrometry/tandem mass spectrometry

Reactive Blue 19 (RB 19), its reactive form (RB 19-VS) and its hydrolyzed form (RB 19-OH) were examined using liquid secondary ion mass spectrometry/tandem mass spectrometry (LSIMS/MS/MS) in the negative-ion mode under low-energy collision conditions (240–300 eV). Structurally characteristic fragment ions were obtained, none of which has been previously reported for these reactive dyes. Among the ions obtained were SO₃^? ions, ions due to central amino cleavage and reactive group cleavage, and ions due to loss of SO₃ and SO₂. Possible pathways for the formation of product ions are proposed. The structural information obtained should help to characterize and identify reactive dyes better.     

Investigation of photocatalytic effect of SnO2 nanoparticles synthesized by hydrothermal method on the decolorization of two organic dyes

Tin oxide nanoparticles about 4 nm in size were successfully synthesized using hydrothermal method. The photocatalytic activity of the particles was determined by the decolorization of malachite green (MG) and titanium yellow (TY) under UV light. 12 ppm of MG and TY were used for the solution with an initial volume of 100 mL. The amounts of catalysts were 10, 30 and 50 mg. The effect of the catalyst loading on the reaction kinetic parameters and the decolorization rate constants (k) were determined. In order to reveal the photocatalytic efficiency of the nano particles, further experiments were conducted with bulk SnO(2). The oxygen species registered no observable effect on the reaction mechanism as nitrogen bubbling leads to no change in decolorization rates. Results showed that the synthesized nano tin oxide particles represent excellent photocatalytic activity for the decolorization of 12 ppm MG under UV light with 150 min of irradiation time. The energies of the highest occupied molecular orbital (HOMO) E(HOMO) of the dyes were also calculated by using the quantum chemical software in order to discuss the differences for the decolorization of two dyes. Electrical energy efficiency values for the decolorization of two dyes were also calculated.     

Use of titanium dioxide photocatalysis on the remediation of model textile wastewaters containing azo dyes

The photocatalytic degradation of two commercial textile azo dyes, namely C.I Reactive Black 5 and C.I Reactive Red 239, has been studied. TiO(2) P25 Degussa was used as catalyst and photodegradation was carried out in aqueous solution under artificial irradiation with a 125 W mercury vapor lamp. The effects of the amount of TiO(2) used, UV-light irradiation time, pH of the solution under treatment, initial concentration of the azo dye and addition of different concentrations of hydrogen peroxide were investigated. The effect of the simultaneous photodegradation of the two azo dyes was also investigated and we observed that the degradation rates achieved in mono and bi-component systems were identical. The repeatability of photocatalytic activity of the photocatalyst was also tested. After five cycles of TiO(2) reuse the rate of colour lost was still 77% of the initial rate. The degradation was followed monitoring the change of azo dye concentration by UV-Vis spectroscopy. Results show that the use of an efficient photocatalyst and the adequate selection of optimal operational parameters may easily lead to a complete decolorization of the aqueous solutions of both azo dyes.     

Sunlight-induced effective heterogeneous photocatalytic decomposition of aqueous organic pollutants to CO2 assisted by a CO2 sorbent, amine-containing mesoporous silica

Photocatalytic mineralization of aqueous formic acid and phenol on pure TiO(2) under sunlight irradiation was substantially accelerated to give a reliable photocatalytic efficiency by conducting the reactions in the presence of a CO(2) sorbent, amine-containing SBA-15, placed in the gas phase of the reactor.     

Modeling and optimization of simultaneous photocatalysis of three dyes on ceramic-coated TiO2 nanoparticles using chemometrics methods: phytotoxicological assessment during degradation process

In this paper, ceramic plates were used as a support of TiO₂ nanoparticles for photocatalytic decolorization of a mixture of three dyes. The three textile dyes (C.I. Basic Red 46, C.I. Basic Blue 3 and Malachite Green) were quantified simultaneously during the photocatalytic degradation process. The partial least squares modeling was successfully applied for the multivariate calibration of the spectrophotometric data. Also, the central composite design has been applied to the optimization of photocatalytic decolorization of the dye solution containing three dyes using an immobilized UV/TiO₂ process. The optimum initial concentration of three dyes, reaction time, and UV light intensity were found to be 5 mg/L, 240 min, and 47.2 W/m², respectively. The chronic phytotoxicity of mixture of dyes was evaluated using aquatic species Spirodela polyrhiza (S. polyrhiza) prior to and after photocatalysis. The phytotoxicity results revealed that the photocatalysis process could effectively reduce the phytotoxicity of the dyes from their aqueous solutions.     

孔道结构H3PW12O40/TiO2的制备及其可见光光催化降解水溶性染料的性能

 采用溶胶-凝胶方法制备了孔道结构复合材料H3PW12O40/TiO2,采用ICP-AES,UV/DRS,31P MAS NMR,TEM和N2吸附等技术对其组成和结构进行了表征. 结果表明,催化剂中活性组分H3PW12O40的基本骨架结构未发生改变,H3PW12O40的担载量为22.29%,催化剂平均粒径为40 nm,具有双孔结构,其平均微孔和介孔孔径分别为0.61和3.06 nm. 考察了催化剂可见光光催化降解6种水溶性染料的性能. 结果表明,6种染料均可不同程度地被降解和矿化. 通过对染料中性红的光催化降解实验,比较了H3PW12O40/TiO2,Degussa P-25和锐钛矿结构TiO2的可见光光催化活性,其中,H3PW12O40/TiO2活性最高,且催化剂最易分离,可循环使用.