Frontiers of Chemical Science and Engineering

ISSN 2095-0179

ISSN 2095-0187(Online)

CN 11-5981/TQ

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EDITORIAL
Message from the Editor
Jingkang WANG
Front Chem Sci Eng. 2011, 5 (1): 1-1.  
https://doi.org/10.1007/s11705-010-0530-9

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REVIEW ARTICLE
Methanation of carbon dioxide: an overview
Wei WANG, Jinlong GONG
Front Chem Sci Eng. 2011, 5 (1): 2-10.  
https://doi.org/10.1007/s11705-010-0528-3

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Although being very challenging, utilization of carbon dioxide (CO2) originating from production processes and flue gases of CO2-intensive sectors has a great environmental and industrial potential due to improving the resource efficiency of industry as well as by contributing to the reduction of CO2 emissions. As a renewable and environmentally friendly source of carbon, catalytic approaches for CO2 fixation in the synthesis of chemicals offer the way to mitigate the increasing CO2 buildup. Among the catalytic reactions, methanation of CO2 is a particularly promising technique for producing energy carrier or chemical. This article focuses on recent developments in catalytic materials, novel reactors, and reaction mechanism for methanation of CO2.

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RESEARCH ARTICLE
Electrospinning of polycarbonate urethane biomaterials
Yakai FENG, Fanru MENG, Ruofang XIAO, Haiyang ZHAO, Jintang GUO
Front Chem Sci Eng. 2011, 5 (1): 11-18.  
https://doi.org/10.1007/s11705-010-1011-x

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Polycarbonate urethane (PCU) nano-fibers were fabricated via electrospinning using N,N- dimethylformamide (DMF) and tetrahydrofuran (THF) as the mixed solvent. The effect of volume ratios of DMF and THF in the mixed solvent on the fiber structures was investigated. The results show that nano-fibers with a narrow diameter distribution and a few defects were obtained when mixed solvent with the appropriate volume ratio of DMF and THF as 1∶1. When the proportion of DMF was more than 75% in the mixed solvent, it was easy to form many beaded fibers. The applied voltage in the electrospinning process has a significant influence on the morphology of fibers. When the electric voltage was set between 22 and 32 kV, the average diameters of the fibers were found between 420 and 570 nm. Scanning electron microscopy (SEM) images showed that fiber diameter and structural morphology of the electrospun PCU membranes are a function of the polymer solution concentration. When the concentration of PCU solution was 6.0 wt-%, a beaded-fiber microstructure was obtained. With increasing the concentration of PCU solutions above 6.0 wt-%, beaded fiber decreased and finally disappeared. However, when the PCU concentration was over 14.0 wt-%, the average diameter of fibers became large, closed to 2 μm, because of the high solution viscosity. The average diameter of nanofibers increased linearly with increasing the volume flow rate of the PCU solution (10.0 wt-%) when the applied voltage was 24 kV. The results show that the morphology of PCU fibers could be controlled by electrospinning parameters, such as solution concentration, electric voltage and flow rate.

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Polymerization of methyl methacrylate catalyzed by mono-/bis-salicylaldiminato nickel(II) complexes and methylaluminoxane
Jihong LU, Danfeng ZHANG, Qian CHEN, Buwei YU
Front Chem Sci Eng. 2011, 5 (1): 19-25.  
https://doi.org/10.1007/s11705-010-0546-1

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Two types of salicylaldiminato-based nickel complexes, mono-ligated Ni(II) complexes ([O-C6H4-o- C(H)=N-Ar]Ni(PPh3)(Ph) (5), [O-(3,5-Br2)C6H2-o-C(H)=N-Ar]Ni(PPh3)(Ph) (6), [O-(3-t-Bu)C6H3-o-C(H)=N-Ar]Ni(PPh3)(Ph) (7)) and bis-ligated Ni(II) complexes ([O-(3,5-Br2)C6H2-o-C(H)=N-Ar]2Ni (8), [O-(3,5-Br2)C6H2-o-C(H)=N-2-C6H4(PhO)]2Ni (9), Ar=2,6-C6H3(i-Pr)2) were synthesized and characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (NMR), mass spectrography (MS) and elemental analysis (EA). In the presence of methylaluminoxane (MAO) as cocatalyst, all the nickel complexes exhibited high activities for the polymerization of methyl methacrylate (MMA) and syndiotactic-rich poly(methyl methacrylate) (PMMA) was obtained. The complexes with less bulky substituents on salicylaldiminato framework possessed higher activities, while with the same salicylaldiminato, the mono-ligated nickel complexes showed higher catalytic activity than bis-ligated ones.

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Performance and synergistic effect of phenolic and thio antioxidants in ABS graft copolymers
Gongsheng LI, Xuhong GUO, Wang NA, Diancheng HAO, Mingyao ZHANG, Huixuan ZHANG, Jun XU
Front Chem Sci Eng. 2011, 5 (1): 26-34.  
https://doi.org/10.1007/s11705-010-0531-8

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The synergistic effect of phenolic and thio antioxidants on the stabilization of acrylonitrile-butadiene-styrene (ABS) graft copolymers has been studied. Three commercial antioxidants Irganox245, Irganox1076 and dilauryl thiodipropionate (DLTP) were selected. Formulations based on hindered phenols and secondary antioxidant DLTP were prepared. Stabilization was monitored in terms of changes in the functional groups (oxidation products), tensile properties and yellowness index. Differential scanning calorimetry (DSC) and thermogravimetry (TG) were also used to assess the stability. The results indicated that the combination of Irganox245 and DLTP showed much better stabilization effect than the individual components due to the strong synergistic effect. Only weak synergism could be observed in the formulation that contained Irganox1076 and DLTP. Irganox1076 and Irgnox1076/DLTP exhibited similar behaviors between antioxidants with the highest and lowest efficiencies.

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Outdoor aging of road asphalt and SBS modified asphalt
Li XIANG, Juan TU, Jian CHENG, Guohe QUE
Front Chem Sci Eng. 2011, 5 (1): 35-42.  
https://doi.org/10.1007/s11705-010-0551-4

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The process of performance degradation of road asphalt (RA) is regarded as aging. At present, better understanding of the thermal-oxidative aging of asphalt is achieved and the corresponding method to evaluate this process is developed; meanwhile, photo-oxidative aging (aging in an atmospheric environment, which is referred to as “outdoor aging” in this paper) of asphalt remains at the initial stages of scientific exploration. The outdoor natural ultraviolet (UV) aging of RA and SBS modified asphalt (SBSMA) are investigated in this study. The experimental results show that the basic performances of RA and SBSMA present similar change tendencies. The softening point increased, while the penetration and ductility decreased as the outdoor aging time passed by, and the 5°C ductility (ductility measured at 5°C) of SBSMA decreased very quickly. The group components of RA and SBSMA also change during UV aging. The content of asphaltene rose and that of aromatics and saturates decreased, while the content of resins changed insignificantly. Moreover, the Fourier transform infrared (FTIR) graphs show that the content of sulfoxide and carbonyl groups in RA and SBSMA increased significantly during the outdoor aging process.

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Synthesis of mono and bis-4-methylpiperidiniummethyl-urea as corrosion inhibitors for steel in acidic media
Abbas TEIMOURI, Nasrin SOLTANI, Alireza Najafi CHERMAHINI
Front Chem Sci Eng. 2011, 5 (1): 43-50.  
https://doi.org/10.1007/s11705-010-0532-7

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Mono and bis-4-methylpiperidiniummethyl urea were synthesized, characterized and used as new corrosion inhibitors of mild steel in the acidic media. Inhibitory effect of two compounds on mild steel surface in the 1 mol·L-1 sulphuric acid has been studied by a series of techniques, such as potentiodynamic polarization, weight loss and quantum chemical calculation methods. Potentiodynamic polarization measurements showed that two inhibitors are mixed type. All measurements showed that inhibition efficiencies enhanced with increase of inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on mild steel surface. Density functional (DFT) calculations have been carried out for the title compounds by performing HF and DFT levels of theory using the standard 6-31G* basis set.

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Preparation of starch esters with crosslinking structures derived from dianhydride
Huijuan CHU, Hongliang WEI, Jing ZHU, Shouyin HU
Front Chem Sci Eng. 2011, 5 (1): 51-54.  
https://doi.org/10.1007/s11705-010-0534-5

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Starch is a kind of natural polymer used in many industrial fields because of its low cost, availability and biodegradation. Potato starch was modified by esterification with pyromellitic dianhydride, and the products were obtained with crosslinking structures. Orthogonal experiments showed that reactive temperature was the primary influencing factor. The product prepared at 40°C for 3 h with the mass ratio of starch and dianhydride of 16∶1 and pH value of 7.5 exhibited a degree of substitution of 11%. FTIR and UV analysis verified the formation of starch esters.

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Synthesis and characterization of norfloxacin biomonomer
Shengxiong DONG, Qiaoping CHEN, Hongfang XIE, Jianhua HUANG
Front Chem Sci Eng. 2011, 5 (1): 55-59.  
https://doi.org/10.1007/s11705-010-0537-2

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A novel drug agent named norfloxacin biomonomer was developed in order to solve the problem of low drug content, uneven drug distribution, low molecular weight, and wide molecular weight distribution of polymer drug, based on polyurethane, which was used as an antibacterial agent to control the bacterial infection associated with biofilm formation on polymeric materials used in biologic environments. In this research, norfloxacin biomonomer was synthesized by esterifying the compound of norfloxacin. High-performance liquid chromatography system was used to analyze the purity of the final product and intermediate products, and Fourier transform infrared spectrometer and mass spectrum were used to verify the final product and intermediate products. The results showed that the objective product was developed successfully. The final product of norfloxacin biomonomer could be incorporated into the polyurethane as chain extender.

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Effects of the SAPO-11 synthetic process on dehydration of ethanol to ethylene
Lina WU, Xiaoxing SHI, Qun CUI, Haiyan WANG, He HUANG
Front Chem Sci Eng. 2011, 5 (1): 60-66.  
https://doi.org/10.1007/s11705-010-0540-7

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The effects of the synthetic condition of SAPO-11 molecular sieves on ethanol dehydration to ethylene were studied. Product-compositions, ethanol conversion, and selectivity to ethylene of synthesized and commercial SAPO-11 molecular sieves were compared. Results are as follows: the optimal synthetic conditions for SAPO-11 molecular sieves are adding pseudoboehmite before orthophoshporic, using di-n- propylamine as the template, having a mass fraction of 40% colloidal silica as the silica source and the starting gel obtained, and running at 200°C for 48 h. From the patterns of NH3-TPD, the amount of acid synthesized by SAPO-11 molecular sieves is less than that by commercial SAPO-11 molecular sieves, and has a stronger weak acid. Also, ethanol conversion and selectivity to ethylene reached 99% at 280°C on synthesized SAPO-11, lower by 20°C compared to commercial SAPO-11. For two SAPO-11 molecular sieves, the by-products in the gas phase are mainly ethane, propane, propene, isobutane, n-butane, propadiene, butylene and some higher hydrocarbons. The by-products in the liquid phase are ethyl ether and acetaldehyde.

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Thermodynamic analysis of liquid phase in situ hydrogenation of glycerol for 1,3-propanediol synthesis
Kun OUYANG, Yu HUANG, Haoyi CHEN, Tao LI, Fahai CAO, Dingye FANG
Front Chem Sci Eng. 2011, 5 (1): 67-73.  
https://doi.org/10.1007/s11705-010-0541-6

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Based on the combination of the glycerol aqueous-phase reforming (APR) and catalytic hydrogenation of glycerol, a novel reaction system of liquid phase in situ hydrogenation of glycerol for the synthesis of 1,3-propanediol is proposed, in which hydrogen is produced from glycerol aqueous-phase reforming in the same reactor. In this new system, the glycerol is the raw material of the aqueous-phase reforming reaction; the hydrogen generated from the APR of glycerol can be quickly transformed to the in situ hydrogenation of glycerol to produce 1,3-propanediol, which can improve the selectivity of hydrogen for the APR process of glycerol. Moreover, thermodynamic calculation of the coupling processes was carried out, and standard molar enthalpies and equilibrium constants of foregoing reactions were obtained. The above calculation results indicate that the combination process is feasible for 1,3-propanediol synthesis.

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Synthesis of poly(maleic acid alkylamide-co-α-olefin-co-styrene) and their effect on flow ability of oils
Jingjing XU, Jun XU, Jie SUN, Shili XING, Li LI, Xuhong GUO
Front Chem Sci Eng. 2011, 5 (1): 74-78.  
https://doi.org/10.1007/s11705-010-0542-5

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To improve the flow ability of crude oil with high content of aromatic asphaltenes, new comb-type copolymers of poly(maleic anhydride-co-α-olefin-co-styrene) (MASCs) with different ratios of maleic anhydride (MA) to styrene were designed and synthesized. 1H NMR and FTIR spectra were used to characterize the chemical structure of the copolymers. The effect of copolymers on the flow ability of model waxy oil and crude oil were studied by rheological method and polarizing light microscopy. Upon the addition of MASCs, the yield stresses of oils were decreased by 1 to 3 orders of magnitude, and the morphology of paraffin crystals were reduced and changed from plates to needles.

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Effect of SiO2/Al2O3 ratio on the conversion of methanol to olefins over molecular sieve catalysts
Qian WANG, Lei WANG, Hui WANG, Zengxi LI, Xiangping ZHANG, Suojiang ZHANG, Kebin ZHOU
Front Chem Sci Eng. 2011, 5 (1): 79-88.  
https://doi.org/10.1007/s11705-010-0550-5

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A series of SAPO-34 molecular sieves with different SiO2/Al2O3 ratios have been synthesized for the methanol-to-olefin (MTO) reaction. Their physico-chemical properties are characterized by various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR) and N2 adsorption-desorption. The results are compared with those of the commercial HZSM-5, which show that the crystallinity and particle diameter of SAPO-34 as well as HZSM-5 increase with SiO2/Al2O3 ratio. The variation of BET surface area of SAPO-34 is different from that of HZSM-5 and the sample with SiO2/Al2O3 ratio of 0.4 exhibits the highest BET surface area. FT-IR spectra indicate that HZSM-5 has both Br?nsted and Lewis acid sites and Br?nsted acid sites are stronger, whereas SAPO-34 samples are dominated only by Lewis acid sites. When the SiO2/Al2O3 ratio increases, propylene and butylenes become the predominant product of the MTO reaction over HZSM-5. In contrast, the main products of this reaction catalyzed by SAPO-34 are ethylene and propylene. According to the product distribution, the reaction mechanism over HZSM-5 catalysts is proposed.

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Gas phase ethylene polymerization over SiO2-supported organosilyl chromate UCC S-2 catalyst using a high-speed stirred-autoclave reactor
Liuzhong LI, Aiyou HAO, Ruihua CHENG, Boping LIU
Front Chem Sci Eng. 2011, 5 (1): 89-95.  
https://doi.org/10.1007/s11705-010-0558-x

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Although an important industrial catalyst for producing high density polyethylene, the SiO2-supported organosilyl chromate UCC S-2 catalyst has not been fully investigated compared with the SiO2-supported oxo chromium Phillips catalyst. In this work, gas phase ethylene polymerization by S-2 catalysts (Cat-1, Cat-2, and Cat-3) was carried out in a high-speed stirred-autoclave reactor. The effects of temperature, time, and pressure on kinetics, activity, and product properties were studied. All kinetics were typical built-up types with slow decay. Compared to the simple physical mixtures of Cat-1 and Cat-2, Cat-3 showed higher activity and its product had a broader molecular weight distribution, indicating new active species induced during blending of Cat-1 and Cat-2 in n-hexane. The innovation by a simple catalyst technology created a new application to meet market demands.

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Emulsification for castor biomass oil
Dongxiang ZHANG, Yuanping LIN, Anmei LI, V. V. TARASOV
Front Chem Sci Eng. 2011, 5 (1): 96-101.  
https://doi.org/10.1007/s11705-010-0553-2

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The effect of the emulsifier formula on the stability of castor oil-water system was studied through compounding three groups of emulsifiers from the aspects of stability factor of absorbance, centrifuge stability, demulsification time in quiescence, appearance of the droplets, and viscosity. The best emulsifier formula for castor biomass oil was the composite formula of sorbitan monooleate and polyoxyethylene sorbitan monostearate. Correlation exists between the stability of emulsion and the viscosity/particle size of the droplets, with better stability in the case of greater viscosity or narrower distribution of particle size in the emulsion of castor oil-water system.

Methanol added to the castor oil-water system may decrease the viscosity of the emulsion. Comparing the castor oil-water emulsion with methanol-castor oil-water emulsion, the optimal hydrophilic and lipophilic balance (HLB) value based on castor oil-water system was acquired between 6.6 and 7.5, while the optimal HLB value based on the methanol-castor oil-water system was between 5.5 and 6.0. The optimal HLB value of methanol-castor oil-water system gradually moved to that of castor oil-water emulsion with adding more water.

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Supercritical carbon dioxide extraction of CLA-ethyl ester
Yingdi CHEN, Peng XU, Jian CHENG
Front Chem Sci Eng. 2011, 5 (1): 102-106.  
https://doi.org/10.1007/s11705-010-0536-3

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Supercritical carbon dioxide (SC-CO2) extraction of Conjugated linoleic acid (CLA) ethyl ester was investigated at pressures in the range of 9 to 10.5 MPa and temperature gradients ranging from 0°C to 21°C. The content of CLA-ethyl ester in the fraction was analyzed with gas chromatography (GC). The experimental results indicated that the rate of extraction would rise with the increase of pressure when temperature gradient was given. Moreover, the extraction pressure had insignificant influence on the selectivity of CLA-ethyl ester in SC-CO2. When pressure was fixed, setting certain temperature gradient can improve the selectivity of CLA-ethyl ester in SC-CO2, and CLA-ethyl ester can be concentrated more effectively than without a temperature gradient. The acid value and peroxide value of the fractions were reduced obviously, compared to the raw material. The optimal condition is pressure at 10 MPa and temperature gradient at 11°C.

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Study on extraction of thiophene from model gasoline with br?nsted acidic ionic liquids
Xiaomeng WANG, Mingjuan HAN, Hui WAN, Cao YANG, Guofeng GUAN
Front Chem Sci Eng. 2011, 5 (1): 107-112.  
https://doi.org/10.1007/s11705-010-0539-0

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Br?nsted acidic ionic liquids (ILs), N-methylimidazole hydrogen sulfate ([HMIm]HSO4) and N-methylpyrrolidone hydrogen sulfate ([HNMP]HSO4), are synthesized and employed as extractants to extract thiophene from model gasoline (thiophene dissolved in n-octane). The effect of extraction temperature, extraction time and volume ratio of ILs to model gasoline on desulfurization rates is investigated. Then, the optimal desulfurization conditions are obtained: the ratio of ILs to model gasoline is 1∶1, extraction temperature is 50°C for [HMIm]HSO4 and 60°C for [HNMP]HSO4, extraction time is 60 min. Meanwhile, the desulfurization rate of [HNMP]HSO4 for model gasoline is 62.8%, which is higher than that of [HMIm]HSO4 (55.5%) under optimal conditions. The reason is discussed on the basis of the interaction energy between thiophene and ILs at the B3LYP/6-311++ G(d,p) level. Furthermore, the total desulfurization rate of [HNMP]HSO4 and [HMIm]HSO4 reaches 96.4% and 94.4%, respectively, by multistage extraction. Finally, the used ILs can be reused by vacuum drying, and their desulfurization rates are not significantly decreased after recycling 7 times in single-stage desulfurization.

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Process study on adsorption of glycerin from saline wastewater by strong base anion resin
Haitao ZHANG, Xiaoqing MA, Xian QU, Jeanpierre Arcangeli
Front Chem Sci Eng. 2011, 5 (1): 113-116.  
https://doi.org/10.1007/s11705-010-0547-0

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A physicochemical method was used to adsorb glycerin in saline wastewater by strong base anion resin (D201). Boric acid, a kind of weak acid, can combine with glycerin, and a specific complex can be produced, which possess bigger molecule than glycerin. Then, this specific complex could be adsorbed by strong base anion resin. Via the experiment, the equation of adsorption isotherm with D201 at 20°C can be shown by lgx/m = 1.74lgCe - 5.72; for column test with simulative glycerin wastewater, the treatment capability was more than nine bed volumes, and 39.77 mg glycerin could be removed by per gram resin. When the NaCl concentration was 10 g/L, five bed volumes of simulative wastewater could be treated, and the adsorb mass was 29.09 mg/g. When the NaCl concentration was 30 g/L, only three bed volumes of simulative wastewater could be treated, and the adsorb mass was 14.83 mg/g.

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HPLC determination of glyoxal in aldehyde solution with 3-methyl-2-benzothiazolinone hydrazone
Yamei ZHU, Xiaoli YAO, Shaohui CHEN, Qun CUI, Haiyan WANG
Front Chem Sci Eng. 2011, 5 (1): 117-121.  
https://doi.org/10.1007/s11705-010-0535-4

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Based on the absorption property of a diazine that can be formed by reaction of glyoxal and 3-methyl-2-benzothiazolinone hydrazone (MBTH) in the Ultraviolet-visible (UV-vis) spectral region, a HPLC method was developed for the determination of glyoxal in acetaldehyde solution. Glyoxal was derivatised from MBTH and the derivatives (diazine) were analyzed by HPLC for identification and quantification. The determination was performed on a ZORBAX Eclipse XDB-C18 column (4.6 × 250 mm, 5 mm) at 35°C with an injection volume of 10 mL, using a mixture of acetonitrile-water solvent (99∶5, v∶v) as a mobile phase with a flow rate of 0.8 mL·min-1. The proper derivative reaction conditions were the temperature of 70°C, MBTH to carbonyl molar ratio of 12, and reaction time of 110 min. The glyoxal diazine was a yellow dye with a maximum molar absorptivity at 401 nm and its retention time was 5.2 min under optimal HPLC conditions. The standard curve for glyoxal had a strong linear relationship with a regression coefficient (R2 = 0.999) in the range of 0.002–0.020 g·L-1. The analysis of glyoxal in an oxidising solution gave accurate results with a relative standard deviation (RSD) value of 0.55%. The average relative recovery was 102%. This efficient HPLC technique is also proposed for detecting other dicarbonyl compounds besides glyoxal.

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Highly effective extraction of oil from soybean by pretreatment of solid-state fermentation with fungi
Xiaojuan NIU, Shuyi QIU, Yuangen WU, Jie YUAN, Yingying XU
Front Chem Sci Eng. 2011, 5 (1): 122-125.  
https://doi.org/10.1007/s11705-010-0533-6

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The solid-state prefermentation by Aspergillus niger (CICC 2377) and Aspergillus flavus (CICC 40536) was employed to increase the oil extraction yield from soybean. The influence of incubation time on oil yield was investigated. The maximum oil yield extracted from the substrate prefermented by Aspergillus niger for 96 h was 23%, which increased by 47.4% compared with control (15.6%). In the same fermentation conditions, the maximum oil yield extracted from substrate prefermented by Aspergillus flavus was 21.6%, which increased by 38.5% compared with control (15.6%). The quality of soybean oil was not changed obviously by the pretreatment of fermentation with fungi.

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Rheological behavior of PMVE-MA aqueous solution with metallic cations
Xiaoping DONG, Li LI, Jun XU, Xuhong GUO
Front Chem Sci Eng. 2011, 5 (1): 126-130.  
https://doi.org/10.1007/s11705-010-0548-z

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The rheological properties of aqueous solutions of poly(methyl vinyl ether-co-maleic anhydride) (PMVE-MA) upon addition of metallic cations at different pH values were investigated. Sol-gel transition and shear-thickening phenomena at moderate shear rate were observed upon increasing the amount of metallic cations, especially for cupric cation. At certain molar ratio (fgel) of added cupric cations to carboxyl groups in PMVE-MA, the system became gel-like, and the storage modulus (G′) and loss modulus (G′′) were parallel and exhibited a power-law dependence on the frequency, which is consistent with Winter’s hypothesis of determining the gel point of a crosslinking system. The shear-thickening behavior depends on fgel, pH, metallic valence, and temperature.

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Spectrokinetics study of probable effects of diverse inorganic ions on bleaching of dye
Rafia AZMAT, Masooda QADRI, Fahim UDDIN
Front Chem Sci Eng. 2011, 5 (1): 131-138.  
https://doi.org/10.1007/s11705-010-0556-z

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Toluidine blue (TB) is an important anticoagulant metachromasia molecule showing a pronounced variation in the visible spectrum due to the aggregation phenomenon and electrostatic interaction with the charged synthetic and biologic polymers. The current study describes the interactive role of diverse inorganic material ions on the bleaching of toluidine blue (tolonium chloride) (TB+) with urea in acidic and basic media using the spectrophotometric technique. The spectra of TB and urea with different cations and anions were monitored and their characteristic features are presented here. The negative effect of added cations on reduction may be the result of altered electron pathways which led to suppression of the reduction/bleaching of TB, while a slight decrease in dye reduction by added anions may be due to the scavenging of the OH* radical. It has been observed in the case of Co2+ that in addition to the electron-transfer reaction, other processes like layer and precipitate formation also appear to be taking place. The dye bleaching process followed pseudo first order kinetics with respect to TB, urea, and H+ ion, whereas significant decoloration in the presence of urea proved that reductants control the redox reaction. No decoloration in acidic medium with diverse ions was seen compared to alkaline media, showing that water pH played an important role in the bleaching of dye. The reduction/bleaching of dye was investigated at different temperatures, and energy parameters were evaluated for a TB+-Urea reaction, including the energy of activation (Ea = 39.60 kJ·mol-1), enthalpy of activation (?H# = 34?kJ·mol-1), entropy of activation (?S# = 146.5 kJ mol-1·K-1), and free energy of activation (ΔG* = -52.35 kJ·mol-1). A mechanism of interaction of diverse ions in dye bleaching and a mechanism of reduction based on the above findings is proposed.

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22 articles