光催化氧化法测定地表水化学需氧量的研究

用溶胶-凝胶法在石英管上制备了纳米TiO₂膜, 并采用光催化氧化法建立了一种测定地表水化学需氧量(COD)的新方法. 以Ce(IV)作为纳米TiO₂光生电子的接受体, 从而减少了纳米TiO₂光生电子和光生空穴的复合, 提高纳米TiO₂的光催化氧化能力. 以测定Ce(IV)的紫外吸收为手段探讨了光催化氧化测定COD的机理, 考察了测定COD的最佳反应条件. 实验结果表明, 该方法条件温和, 不会造成二次污染, 能够实现地表水等低COD值水样的快速准确测定. 在该实验所选择的条件下, 可准确地测定1.0～12 mg?L^－1之间的COD值, 检测限为0.4 mg?L^－1.     

纳米PbO2修饰电极安培检测器流动注射法快速测定化学需氧量

采用以纳米PbO₂修饰电极为工作电极的安培检测器,用流动注射法快速检测水体中的化学需氧量(COD).根据纳米PbO₂修饰电极催化氧化电流的大小测定样品的COD值,在50-1 200 mg/L COD的范围内,电流响应与标准水样中的COD_Cr值呈线性关系,检出限为20 mg/L.该法不需对水样进行预处理,不使用有毒试剂,无二次污染,具有快速、简便、进样量少及工作电极使用寿命长等优点,与COD_Cr国家标准分析法对比具有较好的相关性.     

TiO2-KMnO4体系光催化氧化-光度法测定化学需氧量

基于纳米TiO2和KMnO4协同光催化氧化作用原理,建立了纳米光催化氧化体系测定化学需氧量(COD)的新方法.考察了测定化学需氧量的最佳条件,在含有0.1 g TiO2、 0.002 mol/L KMnO4的50 mL体系中,控温60 ℃,光照反应10 min,COD值在2.5～80 mg/L范围内与KMnO4吸光度变化值ΔA呈线性关系,其相应的线性方程为: ΔA=0.0023 ρ(COD) 0.0137,相关系数R=0.9977,COD值的检出限为1.5 mg/L.用该法测定地表水和自来水的COD值,相对标准偏差分别为1.9%和2.9%,标准加入回收率分别为100.5%和97.0%.     

铕掺杂TiO2的制备及其可见光光催化性能研究

采用溶胶-凝胶法制备了不同铕(Eu)掺杂量的TiO₂纳米颗粒(Eu-TiO₂),利用透射电镜(TEM),X射线光电子能谱(XPS),X射线衍射(XRD)及紫外可见漫反射(UV-Vis DRS)等方法对Eu-TiO₂进行了物理特性的初步表征.结果表明:与未掺杂纳米TiO₂比较,Eu-TiO₂禁带宽度变窄,具有可见光光催化活性.在可见光下(λ≥420 nm)照射下,以光催化降解染料罗丹明B(Rhodamine B,RhB)为目标反应,探讨了Eu-TiO₂不同制备条件对RhB降解光催化活性的影响,优化得到制备高活性Eu-TiO₂最佳pH为3、掺杂比例(n_Eu/n_Ti)为0.05%、煅烧温度为500 ℃.研究了可见光照射下Eu-TiO₂降解RhB和无色有机小分子水杨酸(SA)光催化反应条件及降解特性,RhB的12 h深度氧化矿化率为60.2%,SA的8 h降解率达到100%.通过跟踪测定可见光下Eu-TiO₂光催化反应过程中氧化物种的变化,研究了可见光激发Eu-TiO₂光催化反应机理,表明其光催化反应主要涉及羟基自由基(·OH)历程.     

GO/Ag3PO4复合光催化剂的制备、表征及光催化性能

以石墨粉为原料,采用Hummers氧化法合成氧化石墨烯(GO).然后在超声作用下,将不同含量的Ag₃PO₄沉积在GO上,制备了一系列4% (w,质量分数) GO/Ag₃PO₄、8% GO/Ag₃PO₄、16% GO/Ag₃PO₄和32% GO/Ag₃PO₄复合光催化剂.对所制备的光催化剂运用N₂物理吸附、X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、拉曼光谱、傅里叶变换红外(FT-IR)光谱、紫外-可见漫反射吸收光谱(UV-Vis DRS)等手段进行了表征,并在可见光下考察了GO含量对Ag₃PO₄光催化降解甲基橙(MO)的性能.结果表明, GO能够和Ag₃PO₄实现均匀复合.复合GO提高了催化剂的比表面积,改善了催化剂的吸附性能.复合16% GO使Ag₃PO₄光催化活性提高最显著, 120 min内对MO的降解率达到83%,是纯Ag₃PO₄光催化活性的7.5倍. GO能提高催化剂的比表面积,促进光生电子-空穴(e^-/h⁺)的分离,产生更多活性自由基,从而提高Ag₃PO₄光催化的活性和稳定性.     

TiO2担载在新型载体上的光催化电极

介绍了一种将TiO₂光催化剂担载在新型载体上的光催化电极.新型载体是用炭质材料和聚四氟乙烯制备的,它具有电合成H₂O₂的功能.在电流密度为15mA/cm²时,光催化电极不仅具有高达80%的电合成H₂O₂的电流效率,而且该电极的电位处在0.02V(SCE)左右,使载体表面的TiO₂光催化剂获得了约+0.47V的阳极偏压(相对平带电势),对增加TiO₂光催化反应效率十分有益.在具有新型光催化电极的光反应体系中,水中的有机分子受到来自溶液中大量·OH自由基(H₂O₂被紫外光分解的中间产物)的均相氧化(即光化学氧化),以及来自TiO₂表面光生空穴的复相氧化(即光催化氧化).在光化学氧化和光催化氧化的联合作用下,有机分子的矿物化反应速度显著提高.     

部分还原氧化石墨烯-Fe3O4对水中Mn(Ⅱ)的快速去除

采用改进的Hummers法制备了氧化石墨烯(GO), 继而用一步共沉淀法制备了部分还原氧化石墨烯-四氧化三铁复合物(PRGO-Fe₃O₄). 采用X射线衍射(XRD)、 场发射扫描电子显微镜(FESEM)、 X射线能量色散光谱(EDX)、 高分辨透射电子显微镜(HRTEM)、 选区电子衍射(SAED)及傅里叶变换红外光谱(FTIR)等技术对其进行了分析表征; 考察了pH值、 接触时间、 吸附材料用量、 共存物质、 GO的还原、 循环使用次数等因素对Mn(Ⅱ)吸附行为的影响. 结果表明, PRGO-Fe₃O₄中Fe₃O₄颗粒分布均匀, 大小为15~20 nm, 剩磁和矫顽力均很小. 因Fe₃O₄颗粒的锚定作用, 石墨烯片层很薄, 使PRGO-Fe₃O₄对Mn(Ⅱ)表现出高效的吸附性能和良好的循环使用性能: 当pH=7、 PRGO-Fe₃O₄用量为500 mg/g时, 对201.3211 mg/L的Mn(Ⅱ)溶液仅3 min即达吸附平衡, 吸附率和吸附量分别为99.35%和404.49 mg/g, 磁分离仅需10 s, 经5次循环吸附后, 容量保持率为首次的78%. 机理与热力学研究结果表明, 吸附为吸热、 自发的单层化学吸附.     

H2O2、金属离子等对Cr(Ⅵ)离子光催化还原及对敌敌畏农药光催化氧化的影响

以Cr(Ⅵ)离子、敌敌畏农药作为污染物的代表,研究了H₂O₂、金属离子等对Cr(Ⅵ)离子光催化还原及对敌敌畏农药光催化氧化的影响.结果表明,加入少量的H₂O₂对Cr(Ⅵ)离子的光催化还原起阻碍作用,对敌敌畏农药的光催化氧化起促进作用;加入少量的Cu²⁺对Cr(Ⅵ)离子光催化还原及对敌敌畏农药的光催化氧化均起促进作用;加入Zn²⁺、Na⁺对Cr(Ⅵ)离子及敌敌畏农药的光催化降解均无明显的影响;加入甲醇、甲苯对Cr(Ⅵ)离子的光催化还原起促进作用,对敌敌畏农药的光催化氧化起阻碍作用.探讨了H₂O₂、金属离子等对Cr(Ⅵ)离子光催化还原及对敌敌畏农药光催化氧化影响的机理.     

臭氧协同石墨烯/ZnIn2S4光催化降解含油污水的性能

半导体光催化技术因可以利用太阳能、反应条件温和、无二次污染等优点,被认为是一种具有广阔前景的环境污染治理控制技术。为了解决其降解效率低的不足,本文将光催化技术和光氧化技术相结合,实现了对含油污水的高效降解。利用水热法合成了石墨烯/ZnIn₂S₄复合光催化剂,并利用XRD、BET、TEM、XPS、Raman和吸收光谱等技术对石墨烯/ZnIn₂S₄的结构进行了详细的表征,石墨烯的负载不仅可以大幅提升光催化剂的比表面积,同时石墨烯和ZnIn₂S₄之间的相互作用还可以促进光生载流子的迁移和传输。详细评估了石墨烯/ZnIn₂S₄光催化和臭氧光氧化技术协同降解含油污水的性能和稳定性,并考察了石墨烯的含量、光催化剂的用量、不同的方法以及污水的pH值对含油污水降解性能的影响,结果表明光催化和光氧化的协同作用可以在60 min内将初始COD浓度100 mg/L的含油污水降低91%,且表现出较好的稳定性。     

g-C3N4/BiVO4复合催化剂的制备及应用于光催化还原CO2的性能

用简单的超声分散法合成了具有可见光响应的类石墨氮化碳(g-C₃N₄)/BiVO₄复合光催化剂. 采用X射线衍射(XRD), X射线光电子能谱(XPS), 扫描电子显微镜(SEM), 透射电子显微镜(TEM), 紫外-可见(UV-Vis)分光光谱, 傅里叶红外变换(FTIR)光谱, 荧光发射谱(PL)和光电流响应等技术对所制备催化剂进行相关表征. 通过可见光下(λ> 420 nm)光催化还原CO₂的性能来评价样品的光催化活性, 发现不同复合比的催化剂中, 含40% (w) g-C₃N₄的复合催化剂表现出最高的光催化活性, 其催化活性分别为纯g-C₃N₄纳米片和纯BiVO₄的催化活性的2倍和4倍.光催化活性增加的主要原因是g-C₃N₄和BiVO₄之间形成了异质结, 且相互间能级匹配, 有利于光生电子和空穴的分离.     

纳米TiO2膜用于光催化氧化测定化学需氧量的研究

A photocatalytic oxidation method for determination of chemical oxygen demand （COD） using nano-TiO2 film, based on the use of a nano-TiO2-Ce（SO4）2 system and electrochemical detection, was proposed. The technique was originated from the direct determination of the Ce（Ⅲ） concentration change resulting from photocatalytic oxidation of organic compounds. Ce（Ⅲ）, which was produced by photocatalytic reduction of Ce（SO4）2, could be measured at a multi-walled carbon nanotubes （MWNT） chemically modified electrode （CME）. The COD values by this method were calculated from the differential pulse voltammetry （DPV） current of Ce（Ⅲ） at the CME. Under the optimal operation conditions, the detection limit of 0.5 mg·L^-1 COD with the linear range of 1-600 mg·L^-1 was achieved. This method was also applied to determination of various COD of ground water and wastewater samples. The resuits were in good agreement with those from the conventional COD methods, i.e., permanganate and dichromate ones.     

Preparation of photocatalytic nano-ZnO/TiO2 film and application for determination of chemical oxygen demand

A composite nano-ZnO/TiO₂ film as photocatalyst was fabricated with vacuum vaporized and sol-gel methods. The nano-ZnO/TiO₂ film improved the separate efficiency of the charge and extended the range of spectrum, which showed a higher efficiency of photocatalytic than the pure nano-TiO₂ and nano-ZnO film. The photocatalytic mechanism of nano-ZnO/TiO₂ film was discussed, too. A new method for determination of low chemical oxidation demand (COD) value in ground water based on nano-ZnO/TiO₂ film using the photocatalytic oxidation technology was founded. This method was originated from the direct determination of the Mn(VII) concentration change resulting from photocatalytic oxidation of organic compounds on the nano-ZnO/TiO₂ film, and the COD values were calculated from the absorbance of Mn(VII). Under the optimal operation conditions, the detection limit of 0.1 mg l⁻¹, COD values with the linear range of 0.3-10.0 mg l⁻¹ were achieved. The results were in good agreement with those from the conventional COD methods.     

Study on photocatalytic oxidation for determination of chemical oxygen demand using a nano-TiO2-K2Cr2O7 system

A photocatalytic method for the determination of chemical oxygen demand (COD) using a nano-TiO₂-K₂Cr₂O₇ system is described. The measuring principle is based on direct determination of the change of Cr(III) concentration resulting from photocatalytic oxidation of organic compounds and simultaneous photocatalytic reduction of stoichiometrically involved K₂Cr₂O₇ in the solution. The operation conditions were optimized. The determinative COD value using this method was calculated from the absorbance of Cr(III). The operational characteristics of this method were demonstrated by use of a standard glucose solution as substrate. This method was also applied to the determination of the COD of wastewater samples. The results were in good agreement with those from the conventional (i.e., dichromate) COD methods.     

A surface-fluorinated-TiO2-KMnO4 photocatalytic system for determination of chemical oxygen demand

A new method for chemical oxygen demand (COD) determination has been developed, based on photocatalytic oxidative degradation by using a fluorinated-TiO₂-KMnO₄ system. In such a system, a linear correlation is observed between the amount of oxidizable dissolved organic matter and the amount of MnO₄⁻ consumed by the coupled reduction process. Thus, the COD determination is transformed to a simple and direct determination of the deletion of MnO₄⁻. The surface fluorination of TiO₂ nanoparticles can enhance the rate of photocatalytic oxidation of organic matter and the rate of coupled photocatalytic reduction of MnO₄⁻. This makes the method be rapid, environment friendly and easy for operation. Under optimized conditions, this method can respond linearly to COD of potassium hydrogen phthalate (KHP) in the range of 0.1-280 mg L⁻¹, with a detection limit of 0.02 mg L⁻¹ COD. The COD in samples of tap water, lake water and paper industry sewage has been determined satisfactorily by using this method.     

Optimization of conditions for the determination of the organic matter content of waters by reagentless oxithermography and its application to the analysis of natural waters

To determine the chemical oxygen demand (COD) of water by oxithermography, we studied a high-temperature reactor with two inputs of the gas flow. Such a design allowed the creation of an internal circuit of the oxygen–inert gas (argon) binary flow in the reactor for the oxidation of organic substances and the determination of COD by the decrease in the concentration of oxygen in the binary mixture. The optimum operation parameters of the instrument, affecting the analytical characteristics of the method, were determined. The detection limit for a water sample of the volume 10 µL was 3.4 mg O/L. It was shown that the oxithermograph and the proposed procedure can be used for the determination of COD in drinking and natural waters of Bryansk oblast. The approach developed has an advantage, consisting in the reagentless rapid determination of the COD of waters without preliminary sample preparation.     

纳米二氧化钛膜光催化分解-电化学法联用测定水体中的总磷

利用电化学方法制备了磷钼酸修饰电极,该修饰电极对溶液中的PO43-有很好的电流响应,继而提出了一种用纳米TiO2-K2S2O7共存体系光催化氧化有机磷生成正磷,然后以磷钼酸修饰电极进行测定的新方法。实验中以有机膦酸为标准物质,研究了测定机理,优化了测定条件。实验表明,本方法操作简单、快速、准确。PO43-在0.04~16 mg/L浓度范围内,与修饰电极上的电流响应呈线性关系,检出限为0.02 mg/L。用本方法测定实际水样与标准分析方法所得结果相近。     

A combined photocatalytic determination system for chemical oxygen demand with a highly oxidative reagent

This study focuses on the proposal and validation of a combined photocatalytic (PC) system and a three-parameterized procedure for the determination of chemical oxygen demand (COD; PcCOD(combined)), with a highly oxidative reagent utilized as a photoelectron scavenger and signal indicator. The PcCOD(combined) was the functional combination of photon-efficient thin-layer photocatalytic oxidation, conventional bulk-phase photocatalytic oxidation and photocarrier-efficient high-activity photocatalytic reduction in one single photodigestion system, and consequently, this system possessed high photon-utilization efficiency, automatic stirring function and satisfactory determination characteristics. In comparison with the conventional one-parameterized procedure, the three-parameterized procedure introduces the blank and total photocatalytic reduction responses as two of the three significant analytical parameters. Under the optimized pH value of 3.0-4.5 and a rotating rate of 40 rpm, the representative KMnO(4) species was used for the PcCOD(combined) system as the combined high-activity oxidant, and a narrow and reliable analytical linear range of 0-260 mg L(-1) was achieved during the 10 min duration of the determinations. No observable interference of Cl(-) was found at concentration of the ion up to 2000 mg L(-1). A real sample analysis indicated that the measured values for the PcCOD(combined) were all within a relative deviation below 5% of COD(Cr) of the standard method, which further validates the practical feasibility of the proposed PcCOD(combined) system.     

Study on photocatalytic oxidation for determination of the low chemical oxygen demand using a nano-TiO2-Ce(SO4)2 coexisted system

A new photocatalytic system, nano-TiO₂-Ce(SO₄)₂ coexisted system, which can be used to determine the low chemical oxygen demand (COD) is described. Nano-TiO₂ powders is used as photocatalyst in this system. The measuring method is based on direct determination of the concentration change of Ce(IV) resulting from photocatalytic oxidation of organic compounds. The mechanism of the photocatalytic oxidation for COD determination was discussed and the optimum experimental conditions were investigated. Under the optimum conditions, a good calibration graph for COD values between 1.0 and 12 mg l⁻¹ was obtained and the LOD value was achieved as low as 0.4 mg l⁻¹. When determining the real samples, the results were in good agreement with those from the conventional methods.     

Determination of chemical oxygen demand in fresh waters using flow injection with on-line UV-photocatalytic oxidation and spectrophotometric detection

A flow injection manifold incorporating UV-photocatalytic oxidation for the determination of chemical oxygen demand (COD) in freshwater is reported. The method utilises the UV-photocatalytic oxidation of organic compounds instead of conventional heating (used in the standard method), with acidified potassium permanganate as the oxidant. Sodium oxalate, d-glucose and potassium hydrogen phthalate were used as COD standards. A 100 microL sample solution was injected into a 0.3 mol L(-1) H2SO4 carrier stream containing 0.1 mol L(-1) (NH4)2SO4, merged with a permanganate solution (8 x 10(-4) mol L(-1)) and passed through a 250 cm FEP (fluoroethylene polymer) photo-reaction coil wound around a 15 W UV lamp. The sample throughput was 30 h(-1), with an LOD (blank plus 3sigma) of 0.5 mg COD L(-1) and a linear range of 0.5-50 mg COD L(-1) (D-glucose, r2 = 0.9966). The method had good precision with relative standard deviations of 2.7% at 5 mg COD L(-1) and 1.2% at 20 mg COD L(-1) (n = 12) for glucose. Results for a COD certified reference material (QC Demand Quality Control Standard) were in good agreement with the certified COD value. Recovery from Tamar River water samples for all three COD standards was 83.0-111.0% and the COD values determined were in good agreement with those of a permanganate index reference method.