Electrochemical oxidation of nitrogen-heterocyclic compounds at boron-doped diamond electrode

Nitrogen-heterocyclic compounds (NHCs) are toxic and bio-refractory contaminants widely spread in environment. This study investigated electrochemical degradation of NHCs at boron-doped diamond (BDD) anode with particular attention to the effect of different number and position of nitrogen atoms in molecular structure. Five classical NHCs with similar structures including indole (ID), quinoline (QL), isoquinoline (IQL), benzotriazole (BT) and benzimidazole (BM) were selected as the target compounds. Results of bulk electrolysis showed that degradation of all NHCs was fit to a pseudo first-order equation. The five compounds were degraded with the following sequence: ID > QL > IQL > BT > BM in terms of their rates of oxidation. Quantum chemical calculation was combined with experimental results to describe the degradation character of NHCs at BDD anode. A linear relationship between degradation rate and delocalization energy was observed, which demonstrated that electronic charge was redistributed through the conjugation system and accumulated at the active sites under the attack of hydroxyl radicals produced at BDD anode. Moreover, atom charge was calculated by semi empirical PM3 method and active sites of NHCs were identified respectively. Analysis of intermediates by GC-MS showed agreement with calculation results.     

A comparative study of the electrochemical oxidation of the herbicide tebuthiuron using boron-doped diamond electrodes

The thiadiazolylurea derivative tebuthiuron (TBH) is commonly used as an herbicide even though it is highly toxic to humans. While various processes have been proposed for the removal of organic contaminants of this type from wastewater, electrochemical degradation has shown particular promise. The aim of the present study was to investigate the electrochemical degradation of TBH using anodes comprising boron-doped (5000 and 30 000 ppm) diamond (BDD) films deposited onto Ti substrates operated at current densities in the range 10-200 mA cm⁻². Both anodes removed TBH following a similar pseudo first-order reaction kinetics with k_app close to 3.2 × 10⁻² min⁻¹. The maximum mineralization efficiency obtained was 80%. High-pressure liquid chromatography with UV-VIS detection established that both anodes degraded TBH via similar intermediates. Ion chromatography revealed that increasing concentrations of nitrate ions (up to 0.9 ppm) were formed with increasing current density, while the formation of nitrite ions was observed with both anodes at current densities ?150 mA cm⁻². The BDD film prepared at the lower doping level (5000 ppm) was more efficient in degrading TBH than its more highly doped counterpart. This unexpected finding may be explained in terms of the quantity of impurities incorporated into the diamond lattice during chemical vapor deposition.     

石墨棒阳极电化学氧化降解甲基橙

以石墨棒为阳极,采用电化学氧化法降解水溶液中甲基橙。通过紫外可见光谱和HPLC分析初步鉴定了甲基橙降解过程中的部分中间产物;通过硝酸银滴定法证明了使用的支持电解质氯化钠能参与并促进氮氮双键和苯环的破坏;通过紫外可见光谱、COD的变化考察了电解质的种类及浓度、电极种类、修饰及形状、槽电压和酸碱度等参数对石墨棒阳极降解甲基橙能力的影响。实验结果表明,以石墨棒为阳极、以石墨棒或者铜环为阴极组成的二维电极体系,和以石墨棒为阳极、以铜环为阴极并填充活性炭组成的三维电极体系,在氯化钠水溶液中均能有效降解甲基橙,20 min后脱色率超过95%,3 h后COD去除率超过90%。     

Photosensitized degradation of caffeine: role of fulvic acids and nitrate

The photolysis of caffeine was studied in solutions of fulvic acid isolated from Suwannee River, GA (SRFA) and Old Woman Creek Natural Estuarine Research Reserve, OH (OWCFA) with different chemical amendments (nitrate and iron). Caffeine degrades slowly by direct photolysis (>170 h in artificial sunlight), but we observed enhanced photodegradation in waters containing the fulvic acids. At higher initial concentrations (10 μM) the indirect photolysis of caffeine occurs predominantly through reaction with the hydroxyl radical (OH) generated by irradiated fulvic acids. Both rate constant estimates based upon measured OH steady-state concentrations and quenching studies using isopropanol corroborate the importance of this pathway. Further, OH generated by irradiated nitrate at concentrations present in wastewater effluent plays an important role as a photosensitizer even in the presence of fulvic acids, while the photo-Fenton pathway does not at neutral or higher pH. At lower initial concentrations (0.1 μM) caffeine photolysis reactions proceed even more quickly in fulvic acid solutions and are influenced by both short- and long-lived reactive species. Studies conducted under suboxic conditions suggest that an oxygen dependent long-lived radical e.g., peroxyl radicals plays an important role in the degradation of caffeine at lower initial concentration.     

水中有机污染物电化学清除的研究进展

介绍利用直接电解发、间接电解和电化学吸附等方法去除水中有机污染物的研究现状,并指出今后的工作方面。     

掺硼金刚石薄膜电极在水处理中应用的研究进展

掺硼金刚石(BDD)薄膜电极作为一种新型的电极材料,在水溶液中电解时具有较宽的电位窗口,在浓酸浓碱中具有很好的耐腐蚀性,其表面不易吸附污染物,与它的同素异构体电极及其他普通电极相比,具有更好的化学、物理性能,从而表现出潜在的功能,近年来被科研人员用于废水处理,并取得了很好的处理效果,对近期BDD薄膜电极的制备、在污水处理中的应用及其进展进行了总结与讨论.     

光电催化氧化法降解藻毒素MCLR

使用DSA阳极,对光电催化氧化降解藻毒素MCLR的效能及其影响因素进行了研究。结果表明,电极表面的TiO2在光催化氧化降解MCLR的过程中发挥了明显的光催化作用。在光降解、电催化氧化、光催化氧化和光电催化氧化4个过程中,光电催化氧化对MCLR和TOC的去除率最高,分别可达100%和13%,并且光电催化氧化的去除率大于光催化氧化和电催化氧化之和,表明后两者的耦合过程产生了一定的协同作用。辐照光源和电流密度存在最佳匹配条件,分别为UVC辐照、电流密度10 mA/cm2和UVA辐照、电流密度1.0 mA/cm2,此条件下光电协同作用最显著。在光电催化氧化过程中,随极板间距增大而出现的去除率下降取决于电催化过程,而不是光催化过程;光电催化氧化MCLR的去除率随其初始浓度增加而减小。     

Degradation of chelating agents in aqueous solution using advanced oxidation process (AOP)

This article presents an overview with critical analysis of technical applicability of advanced oxidation process (AOP) in removing chelating agents from aqueous solution. Apart from the effect of metals for chelating agents as a major influencing factor, selected information such as pH, oxidant’s dose, concentrations of pollutants and treatment performance is presented. The performance of individual AOP is compared. It is evident from our literature survey that photocatalysis with UV irradiation alone or coupled with TiO₂, ozonation and Fenton’s oxidation are frequently applied to mineralize target pollutants. Overall, the selection of the most suitable AOP depends on the characteristics of effluents, technical applicability, discharge standard, regulatory requirements and environmental impacts.     

催化湿式氧化技术处理山梨酸生产废水的研究

采用催化湿式氧化技术处理生产山梨酸过程中产生的高浓度有机废水,对催化剂组分进行优选.对反应温度、O2分压(Po2)和废水pH等工艺条件进行考察.实验结果表明:采用自制CuO-Cr2O3-La2O3/TiO2为复合催化剂处理该有机废水时表现出较好的催化活性;在190℃、Po2=2.1 MPa、pH=6.1、COD=10 030.0 mg/L时,反应90 min的COD去除率达到98.3%,而在相同条件下未加催化剂的湿式氧化的COD去除率只有60.1%.     

聚乙烯醇在超临界水氧化中降解

以H2O2为氧化剂用间歇式超临界水氧化装置对聚乙烯醇(PVA)废水进行降解研究。通过正交实验,考察了反应温度、压力、时间及氧化剂过氧倍数对降解效果的影响,并且采用GC/MS对液相降解产物进行表征推测其可能降解途径。结果表明:PVA在SCWO体系中能完全降解,反应温度440℃、压力28 MPa、氧化剂过氧倍数4、反应40 min时,COD去除率为99.03%,出水COD=89.09 mg/L。PVA在SCWO体系中降解为烯烃、烯酮、醇和羧酸类中间产物、最终降解为小分子的饱和直链烷烃类液相产物。     

Electrochemical oxidation of benzene on boron-doped diamond electrodes

This work presents an electrochemical investigation of the benzene oxidation process in aqueous solution on boron-doped diamond (BDD) electrodes. Additionally, in order to determine the main products generated during the oxidation process, electrolysis and high performance liquid chromatography experiments were carried out. The complete degradation of this compound was performed aiming to a further application in waste water treatment. The cyclic voltammetry studies indicate that benzene is irreversibly oxidized in acid medium (H₂SO₄ 0.5 M) on the BDD electrode surface at 2.0 V versus Ag/AgCl in a diffusion controlled process. During the cycling, other products are generated, and a pair of peaks was observed that can be associated with the oxi-reduction of anyone of the following species: hydroquinone, benzoquinone, resorcinol or catechol. The electrolysis experiments were carried out at 2.4 and 2.5 V on the BDD electrode surface in a solution containing 1 × 10⁻² M of benzene (below the saturation concentration in aqueous solution), for 3 and 5 h, respectively. The main products measured were: hydroquinone, resorcinol, p-benzoquinone, catechol and phenol. The complete electrochemical benzene degradation was performed in the electrolysis experiments using a rotating BDD disc electrode (2.5 V for 5 h) and the main products detected were all measured at concentrations lower than 10⁻⁵ M in this condition. The boron-doped diamond electrode had proved to be a valuable tool for the electrochemical degradation of the benzene, a very stable chemical compound.     

光助Fenton氧化法降解水中六氯苯的研究

采用光助Fenton氧化法处理六氯苯模拟废水,考察了反应时间、Fe3 与H2O2摩尔比、Fenton试剂用量、初始pH、六氯苯初始浓度、光强对六氯苯降解效果的影响,并初步探讨了六氯苯的降解动力学规律.结果表明.光助Fenton法降解六氯苯的最佳工艺条件为:紫外灯功率为300 W、Fe3 投加量为1.0 mmol/L、H2O2投加量为5.0 mmol/L、反应时间为60 min、初始pH为3,在此条件下,浓度为500μg/L的HCB的去除率可达91.3%.UV辐射与Fenton氧化对HCB的降解具有协同效应.光助Fenton法对HCB的降解符合一级反应动力学方程,表观速率常数为0.04 min-1,与Fenton法相比,提高了近9倍.     

紫外催化湿式氧化工艺降解油墨废水

为了解决传统催化湿式过氧化氢氧化技术需要高温高压等苛刻条件的问题,将紫外引入催化湿式氧化技术,得到可在常温常压条件下进行的紫外催化湿式氧化工艺(UV-CWOP)。以Cu2+为催化剂,采用该工艺处理油墨废水取得了良好的效果。通过单因素实验确定的最佳工艺条件为:pH值=3,H2O2用量为1.5倍理论量,CuSO4.5H2O投量2 g/L,初始温度40℃。在此条件下处理油墨废水3 h,COD可从9 500 mg/L降解到89 mg/L,出水达到国家《污水综合排放标准》(GB8978-1996)一级标准。     

电化学氧化法去除微污染水中的氨氮

以低氯离子浓度下微污染水中的氨氮(NH4+-N)为研究对象,采用电化学氧化法对污染水中的氨氮进行去除。通过静态和正交实验得到了极板的最佳运行参数。实验结果表明:Cl-浓度在各影响因素中对NH4+-N去除影响最大,且在其他影响因素不变的条件下,通过改变电解电流是解决动态运行时NH4+-N去除率下降较经济有效的方法。最佳运行工艺条件为:电流密度10 mA/cm2,电解时间10 min,极板间距1 cm,溶液初始pH为7,Cl-浓度100 mg/L,面体比102 m2/m3,氨氮的平均去除率在80%以上。     

高级氧化技术降解水中有机磷农药的研究进展

综述了近年来发展迅速的高级氧化技术,主要包括臭氧高级氧化技术、光催化氧化法、超声降解法、电化学水处理技术和超临界水氧化法等.结合有机磷农药废水处理方法的进展,介绍了各种高级氧化技术在机理研究和应用方面取得的成果和存在的问题,并指出了高级氧化技术在有机废水处理方面所具有的潜力.     

电化学氧化法去除超高盐榨菜废水中的氨氮

采用电化学氧化法去除超高盐榨菜废水中的氨氮,阳极为Ti/RuO2-TiO2-IrO2-SnO2网状电极,阴极为网状钛电极,考察了电流密度、电解时间、极板间距、初始pH以及极水比对氨氮去除率的影响,并分析了电流密度对氨氮能耗和阳极效率的影响。结果表明,在初始氨氮浓度为472.73 mg/L,电流密度为156 mA/cm2,极板间距为1.5 cm,极水比为0.8dm2/L,原水pH为4.3～5.0时,电解30 min和60 min时氨氮的去除率分别为89.75%和99.94%,电解30 min时,氨氮能耗最低为96 kWh/kg,阳极效率最高为8.47 g/(h.m2.A)。     

电化学氧化与生物法联合降解木质素的影响因素

采用高效的电化学氧化技术联合低成本的生物降解技术,进行了木质素的降解探索。考察了电流密度、电量、初始pH和电解质浓度对木质素降解效果的影响,结果表明,电流密度和电量影响显著,而初始pH和电解质浓度的影响较小。经过综合比较,得到电化学与生物联合降解木质素的最佳反应条件为:电流密度为5.0 mA/cm2;电量为20 kC;初始pH为7;电解质浓度为0.1 mol/L。在此条件下,碱木质素和木质素磺酸钠的COD去除率分别达到65.97%和59.31%,表征木质素酚羟基结构的UV280分别降低了65.97%和59.77%,色度去除率分别为74.15%和58.32%。总之,电化学前处理可破坏木质素的关键结构,提高木质素的可生化性,从而促进加快后续生物降解。     

电化学氧化法处理含盐苯醌模拟废水

利用钛基二氧化铅电极(Ti/PbO2)作为电催化活性阳极,通过电化学氧化技术对苯醌进行降解矿化,考察常见共存无机盐对苯醌废水降解效率的影响。结果表明,NaCl存在下苯醌废水溶液的COD去除率相比硝酸盐提高了62%,相比硫酸盐提高了45%,NaCl能够显著增强电氧化去除苯醌的电流效率。苯醌的降解对氯离子非常敏感,存在少量的氯离子即可以引起氧化效率明显增加。氯离子浓度越高,苯醌模拟废水的COD去除率越高;但当氯离子浓度高于0.3 mol·L-1时,COD去除率反而有所下降。pH为8的弱碱性环境更有利于含氯离子苯醌废水的电氧化降解反应。提高电流密度可增大COD去除率;但升高温度会降低COD去除率。在pH为8、NaCl浓度为0.3 mol·L-1、电流密度为10 mA·cm-2、温度为20 ℃的条件下,初始浓度为100 mg·L-1的苯醌经3 h电化学氧化降解后COD去除率可达80.9%。通过高效液相色谱对电氧化降解苯醌的中间产物进行分析,发现氯离子存在下苯醌的降解速度显著提高,中间产物顺丁烯二酸的生成速度更快,这说明由氯离子生成的强氧化剂对苯醌具有极强的开环能力。     

Parabens abatement from surface waters by electrochemical advanced oxidation with boron doped diamond anodes

The removal efficiency of four commonly-used parabens by electrochemical advanced oxidation with boron-doped diamond anodes in two different aqueous matrices, namely ultrapure water and surface water from the Guadiana River, has been analyzed. Response surface methodology and a factorial, composite, central, orthogonal, and rotatable (FCCOR) statistical design of experiments have been used to optimize the process. The experimental results clearly show that the initial concentration of pollutants is the factor that influences the removal efficiency in a more remarkable manner in both aqueous matrices. As a rule, as the initial concentration of parabens increases, the removal efficiency decreases. The current density also affects the removal efficiency in a statistically significant manner in both aqueous matrices. In the water river aqueous matrix, a noticeable synergistic effect on the removal efficiency has been observed, probably due to the presence of chloride ions that increase the conductivity of the solution and contribute to the generation of strong secondary oxidant species such as chlorine or HClO/ClO ⁻. The use of a statistical design of experiments made it possible to determine the optimal conditions necessary to achieve total removal of the four parabens in ultrapure and river water aqueous matrices.