Kinetics analysis for development of a rate constant estimation model for ultrasonic degradation reaction of methylene blue

Ultrasound has been used as an advanced oxidation method for wastewater treatment. Sonochemical degradation of organic compounds in aqueous solution occurs by pyrolysis and/or reaction with hydroxyl radicals. Moreover, kinetics of sonochemical degradation has been proposed. However, the effect of ultrasonic frequency on degradation rate has not been investigated. In our previous study, a simple model for estimating the apparent degradation rate of methylene blue was proposed. In this study, sonochemical degradation of methylene blue was performed at various frequencies. Apparent degradation rate constant was evaluated assuming that sonochemical degradation of methylene blue was a first-order reaction. Specifically, we focused on effects of ultrasonic frequency and power on rate constant, and the applicability of our proposed model was demonstrated. Using this approach, maximum sonochemical degradation rate was observed at 490 kHz, which agrees with a previous investigation into the effect of frequency on the sonochemical efficiency value evaluated by KI oxidation dosimetry. Degradation rate increased with ultrasonic power at every frequency. It was also observed that threshold power must be reached for the degradation reaction to progress. The initial methylene blue concentration and the apparent degradation rate constant have a relation of an inverse proportion. Our proposed model for estimating the apparent degradation rate constant using ultrasonic power and sonochemical efficiency value can apply to this study which extended the frequency and initial concentration range.     

碳纳米管吸附去除工业废水中亚甲基蓝的研究

研究了碳纳米管作为一种新型吸附剂去除水中亚甲基蓝。考察了溶液pH值、振荡时间、温度等对亚甲基蓝吸附的影响。溶液pH对亚甲基蓝吸附影响较大,动力学数据显示吸附在8h达到平衡。通过对吸附数据拟合,发现在温度为298—338K和浓度为2.5—12.5mg/L的范围内,碳纳米管对亚甲基蓝的吸附等温线均符合弗仑德里希（Feundlich）兰缪儿（Langmuir）吸附等温式。     

钒酸银的合成与光催化降解亚甲基蓝

采用沉淀法合成了Ag3VO4光催化剂,考察了光催化剂用量和亚甲基蓝初始浓度对催化性能的影响.结果表明：当催化剂用量为0.2g/100mL,亚甲基蓝初始浓度不大于15 mg/L时,亚甲基蓝的降解率可达90％以上.     

分光光度法研究膨润土负载型 光催化剂降解亚甲基蓝

以Zn(NO3)2、SnCl4和膨润土为原料,采用沉淀法制备膨润土负载ZnO/SnO2光降解催化剂,用XRD对其结构进行了表征.在可见光下对亚甲基蓝染料废水进行降解实验,讨论了影响亚甲基蓝降解的主要因素.结果表明,光降解催化剂具有优良的光催化活性,在可见光下对浓度为10mg/L亚甲基蓝,30min降解率达到99.5%.     

Sonocatalytic degradation of methylene blue with TiO2 pellets in water

A series of experiments were carried out to study the degradation of methylene blue by the irradiation of ultrasound onto TiO(2) in aqueous solution. A statistically significant decrease in the concentration of methylene blue was observed after 60 min irradiation. While the reduction was 22% of the initial concentration without H(2)O(2), addition of H(2)O(2) significantly enhanced the degradation of methylene blue for the TiO(2) containing system (85% reduction of the initial concentration). The addition of H(2)O(2) had no effect on the methylene blue degradation when the system contained Al(2)O(3). The degradation ratio of methylene blue was dependent on the amount of TiO(2) and also the specific surface area of TiO(2) in the solution. The effects of radical scavenging agents on the degradation of methylene blue were also investigated for the system with TiO(2). It was found that the radical scavenging agents dimethyl sulfoxide (DMSO), methanol, and mannitol suppressed the degradation, with DMSO being the most effective. The effect of pH on the degradation of methylene blue was further investigated. An U-shaped change in the concentration of methylene blue in the presence of TiO(2) was observed along with the change in pH values (pH 3-12), and the highest degradation ratio was observed at around pH 7. In conclusion, ultrasound irradiation of TiO(2) in aqueous solution resulted in significant generation of hydroxyl radicals, and this process may have potential for the treatment of organic dyes in wastewater.     

Sonolytic degradation of endocrine disrupting chemical 4-cumylphenol in water

The sonolytic degradation of endocrine disrupting compound 4-cumylphenol (4-CyP) in aqueous solution was investigated. The influence of operating parameters for sonication process such as 4-CyP initial concentration, frequency, power, pH, temperature and saturating gas was examined. The extent of degradation was inversely proportional to the initial substrate concentration. The rate of 4-CyP degradation was frequency dependent. The degradation rate increased proportionally with increasing ultrasonic power from 20 to 100 W and temperature in the range of 20-50°C. The most favorable degradation pH was acidic media. Destruction in the presence of saturating gas follows the order: argon>air>nitrogen. The 4-CyP degradation was inhibited in the presence of nitrogen gas owing to the free radical scavenging effect in vapor phase within the bubbles of cavitation. The ultrasonic degradation of 4-CyP was clearly promoted in the presence of bromide anions and the promoting effect on degradation increased with increasing bromide concentration. At low 4-CyP concentration (0.05 mg L(-1)), bicarbonate ion drastically enhanced the rate of 4-CyP degradation. Experiments conducted using pure and natural water demonstrated that the sonolytic treatment was more efficient in the natural water compared to pure water.     

分光光度法研究插层膨润土负载掺氮TiO2光催化剂对亚甲基蓝的光降解

采用溶胶-凝胶法制备了具有高活性的可见光响应插层膨润土负载掺氮TiO₂光催化剂（以下简称光催化剂）。利用IR对光催化剂的微观结构进行表征,并以亚甲基蓝为目标降解物,讨论了光催化剂在可见光下的催化活性。结果表明:氮掺杂TiO₂成功负载于插层膨润土片层表面。在尿素掺杂量为0.35g和催化剂用量为40mg条件下,光催化剂对25mL初始浓度为5mg/L的亚甲基蓝溶液的降解率可达99%。     

Bio-Adsorbent from Carboxymethyl Cellulose and Tannin for Dye Adsorption

A bio-adsorbent was prepared by the crosslinking reaction of a tannin based phenolic resin and carboxymethyl cellulose with epichlorohydrin as crosslinker. The water absorption ratio of the adsorbent decreased due to the introduction of the phenolic resin based on tannin but the adsorption properties of the adsorbent for methylene blue were improved due to the introduction of the phenolic hydroxyl groups from the tannin in comparison with the carboxymethyl cellulose based adsorbent cross-linked with epichlorohydrin. The maximum adsorption capacity of the adsorbent for methylene blue was 1300mg/g and the adsorption process for methylene blue was exothermic. The adsorption ratio of the adsorbent for methylene blue was over 98% for an adsorbent dosage of 2.5 g/L when the concentration of methylene blue in solution was lower than 2000mg/L. The adsorbent can process wastewater containing methylene blue in the pH range of 4–12.     

分光光度法研究粉煤灰对亚甲基蓝的吸附及其机理研究

以龙岩雁石火电厂粉煤灰对亚甲基蓝进行吸附实验,探讨了改性粉煤灰、粉煤灰用量、吸附时间、温度对亚甲基蓝吸附的影响。当粉煤灰投加量为4g/L,亚甲基蓝浓度15mg/L,常温条件下,在60min左右,亚甲基蓝降解率达到了98%以上。结果表明,利用粉煤灰处理亚甲基蓝,具有处理效果好、简单,经济等特点。利用Freundlich等温式和Langmuir等温式对其吸附行为进行描述,表明粉煤灰易于吸附亚甲基蓝,吸附属于化学吸附;用颗粒内扩散方程和准二级吸附动力学方程对实验数据进行回归分析,更好地描述亚甲基蓝在粉煤灰上的吸附。准二级吸附动力学方程能够反映亚甲基蓝在粉煤灰上的吸附机理,准二级吸附速率常数k2=0.5758g/(mg.min)。本研究为粉煤灰处理印染废水提供了理论依据和实践依据。     

Sonochemical degradation of trimethoprim in water matrices: Effect of operating conditions,identification of transformation products and toxicity assessment

The sonochemical degradation of trimethoprim (TMP), a widely used antibiotic, in various water matrices was investigated. The effect of several parameters, such as initial TMP concentration (0.5–3 mg/L), actual power density (20–60 W/L), initial solution pH (3–10), inorganic ions, humic acid and water matrix on degradation kinetics was examined. The pseudo-first order degradation rate of TMP was found to increase with increasing power density and decreasing pH, water complexity (ultrapure water > bottled water > secondary wastewater) and initial TMP concentration.TMP degradation is accompanied by the formation of several transformation products (TPs) as evidenced by LC-QToF-MS analysis. Nine such TPs were successfully identified and their time-trend profiles during degradation were followed. An in silico toxicity evaluation was performed showing that several TPs could potentially be more toxic than the parent compound towards Daphnia magna, Pimephales promelas and Pseudokirchneriella subcapitata.     

Ultrasonic degradation, mineralization and detoxification of diclofenac in water: Optimization of operating parameters

The 20 kHz ultrasound-induced degradation of non-steroidal, anti-inflammatory drug diclofenac (DCF) was investigated. Several operating conditions, such as power density (25–100 W/L), substrate concentration (2.5–80 mg/L), initial solution pH (3.5–11), liquid bulk temperature and the type of sparging gas (air, oxygen, argon), were tested concerning their effect on DCF degradation (as assessed measuring absorbance at 276 nm) and hydroxyl radicals generation (as assessed measuring H₂O₂ concentration). Sample mineralization (in terms of TOC and COD removal), aerobic biodegradability (as assessed by the BOD₅/COD ratio) and ecotoxicity to Daphnia magna and Artemia salina were followed too.DCF conversion is enhanced at increased applied power densities and liquid bulk temperatures, acidic conditions and in the presence of dissolved air or oxygen. The reaction rate increases with increasing DCF concentration in the range 2.5–5 mg/L but it remains constant in the range 40–80 mg/L, indicating different kinetic regimes (i.e. first and zero order, respectively). H₂O₂ production rates in pure water are higher than those in DCF solutions, implying that decomposition basically proceeds through hydroxyl radical reactions. Mineralization is a slow process as reaction by-products are more stable than DCF to total oxidation; nonetheless, they are also more readily biodegradable. Toxicity to D. magna increases during the early stages of the reaction and then decreases progressively upon degradation of reaction by-products; nevertheless, complete toxicity elimination cannot be achieved at the conditions in question. Neither the original nor the treated DCF samples are toxic to A. salina.     

CdS/膨润土复合材料的制备及其光催化性能

以CdCl₂和硫代乙酰胺为反应物,通过湿化学法合成CdS/膨润土复合材料,采用X射线衍射(XRD)、红外光谱(FTIR)以及紫外可见光谱(UV-Vis)等分析技术对其结构及光学性能进行表征。以罗丹明B和亚甲基蓝为目标污染物,考察了CdS/膨润土复合材料对有机染料的降解性能。结果表明:在罗丹明B和亚甲基蓝的初始浓度为20 mg/L 时,光照3 h后,CdS/膨润土对它们的降解率分别为80.6%和88.3%,优于CdS及膨润土原土催化剂。     

气液滑动弧等离子体降解高浓度有机废水的研究

采用气液滑动弧放电非平衡等离子体进行降解高浓度苯酚模拟废水(初始浓度为872 mg／L)的研究。实验研究表明:由于液滴的存在改变了电极间的介电常数和局部电场,气液滑动弧放电的电压波形比纯气流滑动弧放电更加不规则,起弧电压更低;采用氧气作为载气能提高苯酚的降解效果,最后TOC值为44 mg／L;增大气液混合比,相应的加强了废水的雾化效果,增大水气接触表面积,进而提高了苯酚的降解效果;在尾气中检测到CO2的存在,最高浓度达到35357 mg/m3。     

燃煤底灰-微波法降解亚甲基蓝的研究

燃煤底灰中含有丰富的金属,这些金属在微波作用下可以对有机物进行有效降解,燃煤底灰-微波法降解亚甲基蓝溶液主要是通过羟基自由基来降解有机物的。底灰中的金属及稀有金属可以作为深度氧化有机物的催化剂,可降低处理成本、减少环境污染。考查了燃煤底灰用量、H₂O₂用量、以及微波时间对亚甲基蓝降解效率的影响,并测定了亚甲基蓝溶液处理前后的紫外可见光谱。结果表明,亚甲基蓝在燃煤底灰与H₂O₂微波条件下降解率接近100%。燃煤底灰的用量增加可以加快反应进程,增加亚甲基蓝的降解;H₂O₂的增加可以提供更多的·OH,加快反应进程,但当增加到一定量后,对反应进程的影响减弱;微波时间的加长可以提高反应温度,促使亚甲基蓝完全降解。对于0.125 g·L-1的亚甲基蓝,加入1.0 g燃煤底灰、5 mL H₂O₂在中温微波下反应4 min即可全部降解。     

氮气对电晕放电等离子体降解甲基蓝的影响

电晕放电等离子体技术是近年发展起来的一种新型高级氧化工艺,因其处理效果好、操作简单、占地面积小的特点在印染废水处理领域得到了广泛应用。目前因大部分有机污染物的降解机理不详,该技术尚处于探索阶段。因此,为了尽早将电晕放电等离子体技术应用于工业印染废水的处理,不同污染物降解机理的研究对该技术的工业化和产业化应用具有重要意义。至今,电晕放电等离子体技术对研究较多的染料的降解效果均较好,然而,是否适合所有染料的降解有待进一步研究。采用电晕放电等离子体技术处理三苯甲烷类染料甲基蓝,研究了溶液的初始浓度对甲基蓝紫外-可见光谱中芳香环的降解率、发色基团吸光度变化的影响,测定了溶液的浓度、总有机碳（TOC）、总氮（TN）、pH值等指标随着放电时间的变化,并对其相关性进行了分析。结合紫外-可见光谱（UV-Vis）、三维荧光光谱（3D-fluorescence）和傅里叶变换红外光谱（FTIR）三种光谱学手段分析了电晕放电降解甲基蓝过程溶液的颜色、荧光物质和官能团变化,分析了电晕放电降解甲基蓝30 min后生成的中间产物。结果表明：电晕放电等离子体降解甲基蓝过程,溶液的浓度随着放电时间的延长逐渐减小,表明该技术对甲基蓝溶液有一定的降解能力;降解过程高压电极放电击穿含有大量氮气的空气产生N,NO·,N+₂等含氮高活性粒子,这些粒子通过扩散作用迁移至液相,使得溶液中TN含量在整个降解过程逐渐升高;另有部分含氮高活性粒子与钨钢针电极溶出的C元素键合生成发色的CN双键,使得溶液中的总有机碳在放电5 min时有所升高。延长反应时间产生的高活性粒子与溶液中的有机物（甲基蓝及中间产物）继续作用,部分有机物矿化生成CO₂,引起溶液中TOC含量的下降。电晕放电相同时间内产生的活性粒子数量相当,增大甲基蓝浓度,未被降解的甲基蓝分子越多,导致甲基蓝降解率的减小。电晕放电过程甲基蓝分子之间的聚合与发色CN双键的生成共同促使甲基蓝发色基团吸光度在放电5 min时达到最大;且甲基蓝溶液的初始浓度越高,吸光度（A₅-A₀）升高的越多。概括来说,甲基蓝结构中发色CN双键的存在是电晕放电等离子体降解甲基蓝过程溶液颜色加深再变浅的主要原因。反应过程羟基自由基的消耗导致放电5 min时溶液的pH值升高;随着反应的进行溶液中生成的硝酸及小分子酸增强了溶液的酸性,导致pH值降低。三维荧光光谱结果表明,甲基蓝降解过程出现了三类明显的荧光峰,位于E_X/E_M=310~320/430~450,E_X/E_M=240~250/320~340和E_X/E_M=280/340,分别代表腐殖酸类物质、芳香族蛋白质和溶解性微生物代谢副产物。甲基蓝溶液降解前的荧光物质主要为腐殖酸类,随着降解时间的延长,腐殖酸类物质首先降解生成了芳香族蛋白质,进一步降解产生可溶性微生物代谢副产物。比较电晕放电前后甲基蓝溶液的红外光谱图和红外分峰图发现,甲基蓝结构中N-H键3 432.8 cm-1处不对称伸缩振动峰红移了0.3 cm-1,烯烃和苯环上C-H键2 975.9 cm-1处的伸缩振动峰向高波数偏移了0.5 cm-1,1 638.7 cm-1处RCHCHR的双键伸缩振动位置蓝移了3.2 cm-1,芳仲胺的C-N伸缩振动峰1 341.6 cm-1向高波数偏移了1.3 cm-1,磺酸基SO的伸缩振动峰1 121.1和1 034.3 cm-1分别红移了3.8和13 cm-1,甲基蓝结构中的环外CC双键与CN双键吸收峰消失,在1 692.4和1 400.4 cm-1处分别出现了CO和NO的伸缩振动吸收峰,产生了2,5-环己二烯-1,4-二酮、对硝基苯磺酸钠和芳香酮类等中间产物。该结果对于利用电晕放电等离子体技术处理甲基蓝废水具有重要的理论意义和实用价值。     

Comparison of ultrasonic degradation rates constants of methylene blue at 22.8 kHz, 127 kHz, and 490 kHz

Techniques such as solvent extraction, incineration, chemical dehalogenation, and biodegradation have been investigated for the degradation of hazardous organic compounds. We found ultrasound to be an attractive technology for the degradation of hazardous organic compounds in water. However, the effects of ultrasonic frequency on degradation rate constants were not investigated quantitatively. In this study, the degradation process of a model for hazardous organic compound methylene blue was investigated using ultrasonic irradiation. The study focused on the effects of ultrasonic frequency and ultrasonic power on the degradation rate constant. The apparent degradation rate constants were estimated based on time dependence of methylene blue concentration assuming pseudo-first-order kinetics for the decomposition. A linear relationship between the apparent degradation rate constant and ultrasonic power was identified. In addition, the apparent degradation rate constants at frequencies of 127 and 490 kHz were much larger than those at 22.8 kHz. A relationship between the apparent degradation rate constant and the sonochemical efficiency value (SE value) was also found. Based on these results, a simple model for estimating the apparent degradation rate constant of methylene blue based on the ultrasonic power and the SE value is proposed in this study.     

Photocatalytic degradation of methylene blue solution by diphenylanthrazoline compounds

The photocatalytic degradation of methylene blue solution by 8 photocatalytic diphenylanthrazoline compounds was investigated. All diphenylanthrazoline compounds exhibited a good photocatalytic activity towards the methylene blue solution. The removal rate for chemical oxygen demand (COD_Cr) in the methylene blue solution at 12 hours was ~54.1% to 96.3%. 2,8‐Bis(4‐triphenylamino)‐4,6‐diphenyl‐1,9‐anthrazoline ( TM‐2‐d ) was selected for further investigation because of its better photocatalytic activity. To study the optimal reaction conditions for the photocatalytic degradation of dye wastewater, photocatalyst was applied to degrade methylene blue solution. The decolorization rate for simulated dye solutions can exceed 99% in 10 hours, and the COD_Cr removal rate exceeded 91%. These organic semiconductor materials, diphenylanthrazoline compounds, displayed comparative photocatalytic properties to the inorganic semiconductor materials, which can be used in the photocatalytic degradation of organic pollutants.     

Sonocatalytic degradation of methylene blue by a novel graphene quantum dots anchored CdSe nanocatalyst

Cadmium selenide/graphene quantum dots (CdSe/GQDs) nanocatalyst with small band gap energy and a large specific surface area was produced via a facile three-step sonochemical-hydrothermal process. The features of the as-prepared CdSe, GQDs and CdSe/GQDs samples were characterized by photoluminescence spectroscopy (PL), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), Fourier transformed infrared (FT-IR), diffuse-reflectance spectrophotometer (DRS), and Brunauer–Emmett–Teller (BET) analysis. The sonocatalytic activity of the synthesized CdSe/GQDs was effectively accelerated compared with that of pure CdSe nanoparticles in degradation of methylene blue (MB). The influence of the CdSe/GQDs dosage (0.25–1.25 g/L), initial MB concentration (20–30 mg/L), initial solution pH (3–12), and ultrasonic output power (200–600 W/L) were examined on the sonocatalytic treatment of MB aqueous solutions. The degradation efficiency (DE%) of 99% attained at 1 g/L of CdSe/GQDs, 20 mg/L of MB, pH of 9, and an output power of 200 W/L at 90 min of ultrasonic irradiation. Furthermore, DE% increased with addition of K₂S₂O₈ and H₂O₂ as the enhancers via producing more free radicals. However, addition of sulfate, carbonate, and chloride as radical sweeper decreased DE%. Furthermore, well-reusability of the CdSe/GQDs sonocatalyst was demonstrated for 5 successive runs and some of the sonocatalytic generated intermediates were indicated by GC–MS analysis.     

Sonodegradation of 17α-ethynylestradiol in environmentally relevant matrices: laboratory-scale kinetic studies

The sonochemical degradation of 17α-ethynylestradiol (EE2) in secondary treated effluents was investigated. Ultrasound irradiation was provided by a horn-type sonicator operating at 80 kHz. The effect of various operating conditions such as estrogen concentration (25-160 μg/L), power density (18-46 W/L), liquid bulk temperature (15-60 °C), gas sparging (air, oxygen, and helium), solution pH (3 and 7.8), as well as the addition of radical promoters (hydrogen peroxide) or catalysts (TiO₂ and Fe²⁺) on degradation kinetics was evaluated. Changes in estrogen concentration were followed by high performance liquid chromatography and the yeast estrogen screening (YES) assay. EE2 degradation in the range 25-110 μg/L follows first order kinetics in regard to its concentration, while lower order kinetics occur at higher concentrations. The reaction rate increases linearly with applied power and decreases exponentially with temperature at the conditions in question. Continuous sparging of air or oxygen has little effect on the kinetics relative to air-equilibrated conditions, while helium has a marginally positive effect. The inorganic and organic contents of the wastewater matrix appear to promote degradation at inherent conditions in comparison to experiments in ultrapure water. Nevertheless, the addition of H₂O₂ (8.6 and 86 mg/L), Fe²⁺ (2.5-25 mg/L) or TiO₂ (50-2000 mg/L) has no or, in some cases, adverse effect on kinetics.     

Degradation of methylparaben by sonocatalysis using a Co–Fe magnetic carbon xerogel

The degradation of methylparaben (MP) through 20 kHz ultrasound coupled with a bimetallic Co-Fe carbon xerogel (CX/CoFe) was investigated in this work. Experiments were performed at actual power densities of 25 and 52 W/L, catalyst loadings of 12.5 and 25 mg/L, MP concentrations between 1 and 4.2 mg/L and initial pH values between 3 and 10 in ultrapure water (UPW). Matrix effects were studied in bottled water (BW) and secondary treated wastewater (WW), as well as in UPW spiked with bicarbonate, chloride or humic acid. The pseudo–first order kinetics of MP degradation increase with power and catalyst loading and decrease with MP concentration and matrix complexity; moreover, the reaction is also favored at near–neutral conditions and in the presence of dissolved oxygen. The contribution of the catalyst is synergistic to the sonochemical degradation of MP and the extent of synergy is quantified to be >45%. This effect was ascribed to the ability of CX/CoFe to catalyze the dissociation of hydrogen peroxide, formed through water sonolysis, to hydroxyl radicals. Experiments in UPW spiked with an excess of tert-butanol (radical scavenger), sodium dodecyl sulfate or sodium acetate (surfactants) led to substantially decreased rates (i.e. by about 8 times), thus implying that the liquid bulk and the gas-liquid interface are major reaction sites. The stability of CX/CoFe was shown by performing reusability cycles employing magnetic separation of the catalyst after the treatment stage. It was found that the CX/CoFe catalyst can be reused in up to four successive cycles without noteworthy variation of the overall performance of the sonocatalytic process.