Intermediate inhibition in the heterogeneous UV-catalysis using a TiO2 suspension system

Langmuir-Hinshelwood (L-H) kinetic expression was used to develop a basic mathematical model, which could describe the inhibition of intermediates in the photocatalysis of 2-chlorophenol (2-CP) in a suspended TiO2 system. Results showed that the photocatalytic oxidation of 2-chlorophenol followed the L-H type behavior and the reaction by-products displayed an inhibiting effect on the degradation rate. The inhibition was estimated by comparing to observed and estimated half-lives. The higher the initial concentration of 2-chlorophenol, the higher the inhibition of photocatalytic reaction. The L-H kinetic has been modified slightly in this study to rationalize the contrast of inhibited behavior and to improve in favor of a surface reaction. The concentrations of 2-chlorophenol were investigated ranging from 7.78 x 10(-5) to 7.78 x 10(-4) mol l(-1). The degradation of 2-chlorophenol in this reaction condition approximates a first-order kinetics to near-complete degradation. Calculated kinetic profiles are in an excellent agreement with the experimental observation. The results of the theoretical analysis can be used to estimate reaction rates in different initial concentrations of target compound.     

Macro kinetic studies for photocatalytic degradation of benzoic acid in immobilized systems

Semiconductor photocatalytic process has been studied extensively in recent years due to its intriguing advantages in environmental remediation. In this study, a two-phase swirl-flow monolithic-type reactor is used to study the kinetics of photocatalytic degradation of benzoic acid in immobilized systems. Transport contributions into the observed degradation rates were determined when catalyst is immobilized. Intrinsic kinetic rate constants and its dependence on light intensity and catalyst layer thickness, values of adsorption equilibrium constant, internal as well as external mass transfer parameters were determined. The simultaneous effect of catalyst loading and light intensity and optimum catalyst layer thickness were also determined experimentally. Reaction rate constants and overall observed degradation rates were compared with slurry systems.     

Studies on the adsorption and kinetics of photodegradation of a model compound for heterogeneous photocatalysis onto TiO(2)

An investigation was made on the adsorption and kinetics of photodegradation of potassium hydrogenphthalate in an aqueous suspension of TiO(2). Two models, Langmuir and Freundlich, were used to describe the adsorption process and the model proposed by Langmuir-Hinshelwood (L-H) was employed to describe the kinetics of the photodecomposition reactions of hydrogenphthalate. The results of the adsorptions were fitted to the models proposed by Langmuir and Freundlich. Adsorption was found to be a function of the temperature, with adsorption capacity increasing from 2.4 to 4.5 mg/g when the temperature rose from 20 to 30 degrees C. The kinetic model indicates that the rate constant, k, of the first order reaction, is high in the 10.0 to 100 mg/l interval, which is coherent with the low value of the adsorption constant, K. The results fitted to the L-H model led to an equation that, within the range of concentrations studied here, theoretically allows one to evaluate the photodegradation rate.     

Evaluation of relative photonic efficiency in heterogeneous photocatalytic reactors

The evaluation of photonic efficiency in heterogeneous photocatalysis remains elusive because the number of absorbed photons is difficult to assess experimentally. The photonic efficiency of heterogeneous photocatalytic reactors depends on the reactor geometry, irradiation source, and photocatalyst properties. In this work, the relative photonic efficiency of heterogeneous photocatalytic reactors to degrade an azo dye was evaluated using phenol as the standard system. The experimental tests were carried out in a batch reactor under different conditions of pH, catalyst dosage, initial concentration, and ultraviolet (UV) lamps. The kinetics of disappearance of both phenol and azo dye were studied using the initial rate method and were described according to the Langmuir-Hinshelwood (L-H) kinetic model. It was observed that the relative photonic efficiency depends on the adsorption/desorption properties of the photocatalyst.     

Adsorption-oxidation of hydrogen sulfide on activated carbon fibers: effect of the composition and the relative humidity of the gas phase

The removal of hydrogen sulfide by oxidation-adsorption on two type carbon fibers, Actitex FC1201 and RS1301, was studied. Two kinetic steps where identified. During the first step, the degradation appears to be limited by the oxidation reaction. In the second kinetic step, the by-products inhibit the hydrogen sulfide degradation. This leads to a limitation in the carbon site's accessibility and to a lower kinetic. The Langmuir-Hinshelwood model was used to correlate the experimental results and to estimate the kinetic (k) and the Langmuir adsorption (K) constants. For FC1201 fibers, the kinetic constant (k) is five time higher and the adsorption constant is five time lower compared to the RS1301 fibers. The role of the humidity was found to be highly beneficial for the removal of hydrogen sulfide. Especially in the second kinetic step, where it removes the by-product formed and therefore delays the occurrence of this low kinetic step. The kinetic constant (k) is strongly influenced by humidity while the Langmuir adsorption constant (K) seems independent. The effect of the nature of the gas phase on the reaction kinetic was also studied. Under a dry atmosphere, we note that the oxidation-reaction occurs even if the gaseous oxygen is not present. This oxidation is due to the oxygen surface function of the carbon fibers. Moreover, the degradation kinetic is faster under a dry nitrogen atmosphere. The presence of water traces leads to the acidification of the carbon surface, under oxygen or carbon dioxide atmospheres, and hence limits the hydrogen sulfide dissociation. In a humid atmosphere, the oxygen or carbon dioxide leads to a faster reaction kinetic. The acidification of the carbon surface is largely counterbalanced by the dissolution of the by-products.     

Biodegradation of 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT) by using Serratia marcescens NCIM 2919

A solvent tolerant bacterium Serratia marcescens NCIM 2919 has been evaluated for degradation of DDT (1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane). The bacterium was able to degrade up to 42% of initial 50 mg L^?1 of DDT within 10 days of incubation. The highlight of the work was the elucidation of DDT degradation pathway in S. marcescens. A total of four intermediates metabolites viz. 2,2-bis (chlorophenyl)-1,1-dichloroethane (DDD), 2,2-bis (chlorophenyl)-1,1-dichloroethylene (DDE), 2,2-bis (chlorophenyl)-1-chloroethylene (DDMU), and 4-chlorobenzoic acid (4-CBA) were identified by GC-Mass and FTIR. 4-CBA was found to be the stable product of DDT degradation. Metabolites preceding 4-CBA were not toxic to strain as reveled through luxuriant growth in presence of varying concentrations of exogenous DDD and DDE. However, 4-CBA was observed to inhibit the growth of bacterium. The DDT degrading efficiency of S. marcescens NCIM 2919 hence could be used in combination with 4-CBA utilizing strains either as binary culture or consortia for mineralization of DDT. Application of S. marcescens NCIM 2919 to DDT contaminated soil, showed 74.7% reduction of initial 12.0 mg kg^?1 of DDT after 18-days of treatment.     

Photocatalytic degradation of the herbicide erioglaucine in the presence of nanosized titanium dioxide: comparison and modeling of reaction kinetics

The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO2 nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO2 and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO2, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO2 system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir-Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm-1 and 0.984 ppm min-1, respectively. In this work, we also compared the reactivity between the commercial TiO2 Degussa P-25 and a rutile TiO2. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO2 for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO2 process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO2.     

An anaerobic continuous-flow fixed-bed reactor sustaining a 3-chlorobenzoate-degrading denitrifying population utilizing versatile electron donors and acceptors

An anaerobic continuous-flow fixed-bed column reactor capable of degrading 3-chlorobenzoate (3-CBA) under denitrifying conditions was established, and its rate reached 2.26 mM d(-1). The denitrifying population completely degraded 3-CBA when supplied at 0.1-0.54 mM, but its activity was partly suppressed when 3-CBA was supplied at 0.89 mM. Nitrate was concomitantly consumed throughout the operation of the reactor, the amount of which was similar to or up to 35% higher than the theoretical stoichiometric value that was calculated by assuming that 3-CBA degradation is coupled with denitrification. Batch incubation experiments proved that nitrate is strictly required for 3-CBA degradation in the absence of molecular oxygen. The population also degraded 3-CBA aerobically. Benzoate and 4-CBA were degraded under denitrifying conditions as well as 3-CBA, but 2-CBA was not. Considering that the previously reported denitrifying 3-CBA-degrading cultures do not exhibit 4-CBA degradation under denitrifying conditions, nor aerobic 3-CBA degradation [FEMS Microbiol. Lett. 144 (1996) 213, Appl. Environ. Microbiol. 66 (2000) 3446], the microbial population developed in this experiment was physiologically versatile with respect to the utilization of both electron donors and electron acceptors.     

Adsorption kinetics of herbicide paraquat from aqueous solution onto activated bleaching earth

In the present study, the activated bleaching earth was used as adsorbent for the herbicide paraquat adsorption in a batch adsorber. The rate of adsorption has been investigated under the controlled process parameters like agitation speed, initial paraquat concentration, adsorbent dosage and temperature. A batch kinetic model, based on the assumption of a pseudo-second order mechanism, has been tested to predict the rate constant of adsorption, equilibrium adsorption capacity, time of half-adsorption, and equilibrium concentration by the fittings of the experimental data. The results of the kinetic studies show that the adsorption process can be well described with the pseudo-second order equation. Based on the isotherm data obtained from the fittings of the adsorption kinetics, Freundlich model appears to fit the adsorption better than Langmuir model. In addition, the effective diffusion coefficient has also been estimated based on the restrictive diffusion model.     

A geometric approach to determine adsorption and desorption kinetic constants

A geometric method based on Langmuir kinetics has been derived to determine adsorption and desorption kinetic constants. In the conventional procedure, either the adsorption kinetic constant (k(a)c) or desorption kinetic constant (k(d)c) is found from kinetic experiments and the other is calculated by their correlation with the equilibrium constant, i.e, k(d)c = Kcon/k(a)c, where Kcon has been known from equilibrium studies. The determined constants (Kcon, k(a)c, k(d)c), if based only on the conventional procedure, may not be accurate due to their mathematical dependence. Therefore, the objectives of this study are applying a geometric approach to directly determine Langmuir kinetic constants and describe adsorption behavior. In this approach, both adsorption kinetic constant (k(a)g) and desorption kinetic constant (k(d)g) are obtained only from data of kinetic experiments, and a geometric equilibrium constant (Kgeo) is calculated by Kgeo = k(a)g/k(d)g. The deviation between Kgeo and Kcon can prove the accuracy of k(a)g and k(d)g which were determined by this method. This approach was applicable to selenate, selenite and Mg2+ adsorption onto SiO2 regardless of whether the adsorbate formed inner- or outer-sphere complexes. However, this method showed some deviation between Kcon and Kgeo for Mn2+ adsorption because of the formation of surface Mn(II)-hydroxide clusters, which was inconsistent with the basic assumption of this method of monolayer adsorption.     

Kinetic studies of adsorption of lead(ll) from aqueous solution by wine-processing waste sludge.

A waste sludge produced from a wine-processing wastewater treatment process was used as an adsorbent to removal of heavy metal-lead(II) from aqueous solution. Results of kinetic experiments demonstrated that the adsorption was effective and rapid. Four different kinds of adsorption kinetic models (i.e., pseudo-first-order, pseudo-second-order, and two intra-particular mass diffusion models) were used to investigate the adsorption mechanisms. A normalized standard deviation was used to find the best adsorption kinetic model for the removal of lead(ll) by the sludge. The comparison shows that the kinetic adsorption data can be well-described by the pseudo-second-order adsorption model and that sorption might be a rate-limiting control. The adsorption-rate constant and adsorption capacity of pseudo-second-order adsorption equation were calculated. The parameters (initial lead(II) concentration, sludge-particle size, and sludge dosages), which affect the adsorption capacity of sludge, were discussed by using the pseudo-second-order adsorption equation.     

Ru-TiO_2光电极对亚甲基蓝的光电催化降解

采用阳极氧化法制备Ru-TiO2光电极,以该电极为工作电极,石墨作对电极,饱和甘汞电极为参比电极,对亚甲基蓝溶液的光电催化降解进行了研究。结果表明:煅烧温度600℃,掺杂1%Ru的Ru-TiO2光电极催化活性最好;以紫外灯(125 W)为光源,当外加偏压0.2 V,pH为5时,Ru-TiO2光电催化亚甲基蓝120 min可使其完全脱色;亚甲基蓝的光电催化降解遵从Langmuir-Hinshelwood动力学模型,测得其反应速率常数k=0.781 mmol/(L.min),吸附常数K=0.225 L/mmol。     

Competitive adsorption of dye metanil yellow and RB15 in acid solutions on chemically cross-linked chitosan beads

One kind of adsorbent with a high adsorption capacity for anionic dyes was prepared using ionically and chemically cross-linked chitosan beads. A batch system was applied to study the adsorption behavior of one acid dye (MY, metanil yellow) and one reactive dye (RB15, reactive blue 15) in aqueous solutions by the cross-linked chitosan beads. The adsorption capacities was 3.56 mmol g(-1) (1334 mg g(-1)) for dye MY and 0.56 mmol g(-1) (722 mg g(-1)) for dye RB15 at pH4, 30 degrees C. The Langmuir model agreed very well with the experimental data (R(2)>0.996). The kinetics of adsorption for a single dye and the kinetics of removal of ADMI color value in mixture solutions at different initial dye concentrations were evaluated by the nonlinear first-order and second-order models. The first-order kinetic model fits well with the dynamical adsorption behavior of a single dye for lower initial dye concentrations, while the second-order kinetic model fits well for higher initial dye concentrations. The competitive adsorption favored the dye RB15 in the mixture solution (initial conc. (mM): MY=1.34; RB15=1.36); while it favored the dye MY in the mixture solution (initial conc. (mM): MY=3.00; RB15=1.34) and the adsorption kinetics for dye RB15 has the tendency to shift to a slower first order model.     

pH值和碳氮比对亚硝酸型反硝化影响的研究

利用序批式反应器中长期驯化好的以亚硝酸盐为主要基质的纯种污泥，做锥形瓶实验，分别研究pH和碳氮比对亚硝酸型反硝化的影响。结果表明，亚硝酸型反硝化适宜的pH范围在7.7～8.6，最佳pH值在8.2左右；碳氮比（C/N）大于1.94，可实现连续稳定的脱氮效果，起始亚硝氮比基质降解速率随C/N的增加而增加，大于3.11速率几乎不再增加，通过动力学分析，得出该实验条件下C/N的饱和常数Ks为9.36。     

Fe^3＋掺杂TiO2/凹凸棒复合材料的光催化性能

采用酸催化的溶胶-凝胶法制备了一系列Fe^3＋掺杂TiO2/凹凸棒（Fe^3＋-TiO2/ATP）复合光催化剂材料。在可见光条件下,以亚甲基蓝（MB）溶液的光催化降解反应,评价了样品的光催化性能,研究了TiO2负载量、Fe^3＋掺杂量和焙烧温度对复合材料光催化性能的影响。在单因素实验的基础上,采用正交实验设计（L25（53））优化了催化剂的制备条件。光催化实验结果表明,MB在复合材料上的光催化降解反应遵循Langmuir-Hinshelwood（L-H）动力学模型。正交实验结果表明,当TiO2负载量为15%、Fe^3＋掺杂量为0.5%和焙烧温度为550℃时,得到的复合材料对MB的光催化降解效率最佳,测得表观反应速率常数kapp为6.09×10^-3min^-1,反应4 h后MB的降解率（Dt）可达75.88%,相同实验条件下与P25（1.51×10^-3min^-1）相比较,反应速率提高了4.03倍,降解率提高了45.05%。另外,复合材料的沉降性能优于P25,易于分离,是一类有应用前景的复合光催化剂。敏世雄王芳魏立强王永生冯雷佟永纯韩玉琦     

Extended geometric method: a simple approach to derive adsorption rate constants of Langmuir-Freundlich kinetics

A new and simple equation has been presented here for calculation of adsorption and desorption rate constants of Langmuir-Freundlich kinetic equation. The derivation of new equation is on the basis of extension and correction to the geometric method which has been presented by Kuan et al. [Kuan, W.-H., Lo, S.-L., Chang, C.M., Wang, M.K., 2000. A geometric approach to determine adsorption and desorption kinetic constants. Chemosphere 41, 1741-1747] for the kinetics of adsorption/desorption in aqueous solutions. The correction is to consider that the concentration of solute is not constant and changes as adsorption proceeds. The extension is that we applied Langmuir-Freundlich kinetic model instead of Langmuir kinetic model to consider the heterogeneity and therefore it is more applicable to the real systems. For solving Langmuir-Freundlich kinetic model, some geometric methods and also Taylor expansion were used and finally a simple and novel equation was derived (Eq. (20)) for calculation of adsorption rate constant. This new method was named "extended geometric method". The input data of the obtained equation can be simply derived from initial data of adsorption kinetics. Finally the adsorption of methyl orange onto granular activated carbon was carried out at dynamic and equilibrium conditions and the capabilities of extended geometric method were examined by the experimental data.     

Photocatalytic Degradation of the Herbicide Erioglaucine in the Presence of Nanosized Titanium Dioxide: Comparison and Modeling of Reaction Kinetics

The present work mainly deals with photocatalytic degradation of a herbicide, erioglaucine, in water in the presence of TiO₂ nanoparticles (Degussa P-25) under ultraviolet (UV) light illumination (30 W). The degradation rate of erioglaucine was not so high when the photolysis was carried out in the absence of TiO₂ and it was negligible in the absence of UV light. We have studied the influence of the basic photocatalytic parameters such as pH of the solution, amount of TiO₂, irradiation time and initial concentration of erioglaucine on the photodegradation efficiency of erioglaucine. A kinetic model is applied for the photocatalytic oxidation by the UV/TiO₂ system. Experimental results indicated that the photocatalytic degradation process could be explained in terms of the Langmuir–Hinshelwood kinetic model. The values of the adsorption equilibrium constant, K, and the second order kinetic rate constant, k, were 0.116 ppm^{? 1} and 0.984 ppm min^{? 1}, respectively. In this work, we also compared the reactivity between the commercial TiO₂ Degussa P-25 and a rutile TiO₂. The photocatalytic activities of both photocatalysts were tested using the herbicide solution. We have noticed that photodegradation efficiency was different between both of them. The higher photoactivity of Degussa P-25 compared to that of rutile TiO₂ for the photodegradation of erioglaucine may be due to higher hydroxyl content, higher surface area, nano-size and crystallinity of the Degussa P-25. Our results also showed that the UV/TiO₂ process with Degussa P-25 as photocatalyst was appropriate as the effective treatment method for removal of erioglaucine from a real wastewater. The electrical energy consumption per order of magnitude for photocatalytic degradation of erioglaucine was lower with Degussa P-25 than in the presence of rutile TiO₂.     

CNTs/TiO2/CS光降解苯的动力学

综合光催化氧化苯的动力学过程、光辐射场模型和质量守恒定律,采用平板型反应器建立了碳纳米管/二氧化钛/壳聚糖(CNTs/TiO2/CS)催化薄膜光催化氧化气相苯的数学模型;该模型考虑了光强、相对湿度、初始浓度与气体流速对气相苯光降解的影响。结果表明,建立的数学模型与实验结果吻合较好。     

Ru-TiO2光电极对亚甲基蓝的光电催化降解

采用阳极氧化法制备Ru—TiO2光电极，以该电极为工作电极，石墨作对电极，饱和甘汞电极为参比电极，对亚甲基蓝溶液的光电催化降解进行了研究。结果表明：煅烧温度600oC，掺杂1％Ru的Ru-TiO2光电极催化活性最好；以紫外灯（125W）为光源，当外加偏压0．2V，pH为5时，Ru-TiO2光电催化亚甲基蓝120min可使其完全脱色；亚甲基蓝的光电催化降解遵从Langmuir—Hinshelwood动力学模型，测得其反应速率常数k：0．781mmol／（L·min），吸附常数K=0．225L／mmol。     

CNTs/TiO2/CS光降解苯的动力学

综合光催化氧化苯的动力学过程、光辐射场模型和质量守恒定律,采用平板型反应器建立了碳纳米管/二氧化钛/壳聚糖（CNTs/TiO2/CS）催化薄膜光催化氧化气相苯的数学模型;该模型考虑了光强、相对湿度、初始浓度与气体流速对气相苯光降解的影响。结果表明,建立的数学模型与实验结果吻合较好。