Measurement of carbonaceous aerosols: validation of a thermal gravimetric method and its comparison with a thermal optical transmittance method

A high throughput thermal gravimetric method was developed to measure the carbonaceous aerosols and particulates collected on filters. Representative portions or the whole piece of a loaded or blank filter was sampled and conditioned at 105±5 °C for 4 h to drive away water moisture. The sample was then treated at 550±10 °C for 4 h. After each of the heat treatment steps, the sample was conditioned in a humidity and temperature-controlled cabinet for 12 h till constant weight. The weight of the filter before and after the heated treatment was measured and the weight difference between the treatment at 550 and 105 °C was calculated as the weight of the carbon containing substances (CCS). Reference chemical standards and certified reference materials SRM 1649a and 1650a were used to validate the method. CCS concentrations of real aerosol samples collected in the city of Hong Kong during the summer of 2001 were also measured, compared and correlated with the concentrations of total carbon (TC), elemental carbon (EC) and organic carbon (OC) of the samples determined using a thermal optical transmittance (TOT) method as specified in NIOSH method 5040. The weight of organic compounds in airborne particulate matters is usually estimated by multiplying the weight of TC, which is determined by thermal/thermal optical methods, by a factor of 1.2 or 1.4. To this end, a correction factor of approximately 1.6 was found to relate TC to the measured values of CCS in aerosol samples collected in the urban atmosphere of Hong Kong. The proposed procedure for measurement of CCS is simple, easy to follow and requires simple laboratory instrumentation. Typically, the analysis of more than 100 filter samples can be completed within three working days with minimal attention.     

Oligo(fluorenyleneethynylenegermylene)s and their metallopolymers

Oligo(fluorenyleneethynylenegermylene)s and their polyplatinynes are synthesized and photophysically characterized; inclusion of heavy germylene bridges greatly boosts the phosphorescence decay rate in metallopolymers.     

Effects of the molar ratio of hydroxide and fluoride to Al(III) on fluoride removal by coagulation and electrocoagulation

The effect of the molar ratio of hydroxide and fluoride ions to Al(III) ions (gamma(OH) and gamma(F)) on coagulation and electrocoagulation (EC) was studied to solve the problem of the over addition of acid or base. The efficiency of defluoridation was approximately 100% when the sum of gamma(OH) and gamma(F) (gamma(OH+F)) was close to 3. This finding reveals that the fluoride ions and the hydroxide ions can co-precipitate with Al(III) ions and the formula of the precipitate is Al(n)F(m)(OH)(3n-m). However, when gamma(OH) was less than 2.4, the defluoridation efficiency, given that gamma(OH+F)=3, dropped as gamma(OH) fell, because the amount of aluminum polymer formed dropped. The efficiency of defluoridation of EC exceeded that of coagulation for equal gamma(OH) and gamma(OH+F), when gamma(OH+F)>3, proving the existence of an electrocondensation effect.     

Asymptotic Expansions for Second-Order Linear Difference Equations,II

Infinite asymptotic expansions are derived for the solutions to the second-order linear difference equation where p and q are integers, a(n) and b(n) have power series expansions of the form for large values of n, and a₀ ≠ 0, b₀ ≠ 0. Recurrence relations are also given for the coefficients in the asymptotic solutions. Our proof is based on the method of successive approximations. This paper is a continuation of an earlier one, in which only the special case p ≤ 0 and q = 0 is considered.     

Optimal conditions and sample storage for the determination of H2O2 in marine waters by the scopoletin-horseradish peroxidase fluorometric method

The conditions presently in use for the fluorometric determination of H₂O₂ in marine waters, by reacting H₂O₂ with scopoletin in the presence of horseradish peroxidase (HRP) and measuring the quenching of the fluorescence intensity of scopoletin, are not the optimal conditions. Under the optimized conditions of a pH of 8.5–9.5, an excitation wavelength of 390 nm and an emission wavelength of 460, the sensitivity of the method can be increased significantly, by up to more than a factor of 3 and the variations in the sensitivity from sample to sample can be significantly reduced. Furthermore, the samples need not be analyzed immediately after sample collection as presently prescribed. After scopoletin and HRP have been added to a sample immediately after sample collection, the sample may be stored at room temperature in the dark for up to four days before the quenched fluorescence intensity of scopoletin is read.     

离子刻蚀法制备具有高效催化性能的m-Bi2O4/BiOCl p-n异质结催化剂

光催化技术作为一种绿色的环境修复方法而备受关注,它直接利用太阳光作为能源,可有效地降解有机污染物.铋系化合物具有化学稳定性强、抑制光腐蚀、无毒和来源广泛等优点,被认为是一种环境友好的光催化剂,广泛用于降解染料、苯酚和其他有机污染物.BiOCl具有独特的内部结构,可形成内电场促进电子和空穴的移动,抑制其复合.但是BiOCl本身带隙能过大,只能被紫外光激发,对光的利用率较低,限制了其在环境治理中的应用.近两年来发现,m-Bi2O4带隙能小,可吸收大波长的可见光,催化性能好.为充分发挥m-Bi2O4的优异性质,改善BiOCl的性能,本文将BiOCl与m-Bi2O4复合制得新型催化剂,降低催化剂的带隙能,增强对光的吸收,提高量子效率,促进光生载流子的分离,抑制电子-空穴复合,从而提高催化剂性能,加速降解反应进程.本文通过离子刻蚀法制备具有p-n异质结的m-Bi2O4/BiOCl复合催化剂,通过调节HCl的加入量制得不同比例的催化剂,并考察了其在可见光下催化降解MO(甲基橙)的性能.结果表明,m-Bi2O4/BiOCl复合催化剂在可见光下表现出优异的光催化降解MO和四环素的性能,反应10内min可降解95％的MO,反应150 min内四环素的降解率为85.5％;该复合催化剂对MO和四环素的光降解效率分别是纯BiOCl的52.3和4.9倍.活性自由基捕获实验表明,空穴在光催化降解过程中起最主要的作用,其次是超氧自由基,羟基自由基对降解反应也起到一定的作用.采用XRD,SEM,EDS,TEM,SAED,FT-IR,Raman,XPS,BET,UV-vis和光电流等表征方法分析了催化剂的结构、形貌、化学组成、元素价态、孔结构、带隙能、光学性质和载流子复合效率.结果表明,与BiOCl的斜四方体相比,m-Bi2O4/BiOCl复合催化剂呈现纳米片状结构,氯离子进入晶格的内部,颜色也由BiOCl原来的深褐色变为黄色.m-Bi2O4/BiOCl为介孔结构,比表面积为112.90 m2/g,其吸收波长红移,由紫外光扩展至可见光区域,带隙能也由3.2降低为1.87 eV,能带弯曲形成p-n异质结,提高了电子-空穴的转移效率,抑制其复合;m-Bi2O4/BiOCl的光电流密度高于m-Bi2O4和BiOCl,电子-空穴的分离效率更高,因而其催化性能更优越.     

Flower-like Bi2WO6/ZnO composite with excellent photocatalytic capability under visible light irradiation

The photocatalytic ability of ZnO is improved through the addition of flower-like Bi₂WO₆ to prepare a Bi₂WO₆/ZnO composite with visible light activity. The composite is characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy with UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and N₂ adsorption-desorption isotherms. After modification, the band gap energy of Bi₂WO₆/ZnO is reduced from 3.2 eV for ZnO to 2.6 eV. Under visible light irradiation, the Bi₂WO₆/ZnO composite shows an excellent photocatalytic activity for degrading methylene blue (MB) and tetracycline. The photo-degradation efficiencies of (0.3:1) Bi₂WO₆/ZnO for MB and tetracycline are approximately 246 and 4500 times higher than those of bare ZnO, respectively, and correspondingly, the photo-degradation rates for the two pollutants are approximately 120 and 200 times higher than those with bare ZnO, respectively. Moreover, the photocatalyst of (0.3:1) Bi₂WO₆/ZnO exhibits a higher transient photocurrent density of approximately 4.5 μA compared with those of bare Bi₂WO₆ and ZnO nanoparticles. The successful recombination of Bi₂WO₆ and ZnO enhances the photocatalytic activity and reduces the band gap energy of ZnO, which can be attributed to the effective separation of electron–hole pairs. Active species trapping experiments display that [O₂]^? is the major species involved during photocatalysis rather than ?OH and h⁺. This study provides insight into designing a meaningful visible-light-driven photocatalyst for environmental remediation.