TiO<Subscript>2</Subscript> photocatalytic degradation of 4-chlorobiphenyl as affected by solvents and surfactants

Purpose  

TiO₂ photocatalytic degradation of 4-chlorobiphenyl (PCB3) in aqueous solution under UV irradiation was investigated as affected by different environmental factors, including initial PCB3 concentration, TiO₂ content, UV intensity, H₂O₂ concentration, cosolvents, and surfactants.     

Enhanced Photocatalytic Activity of Co Surface Doped Nanocrystalline TiO2-SiO2 Composite Films

In order to enhance the photocatalytic activity of the TiO₂ films, Co surface doped TiO₂-SiO₂ composite films were synthesized by the improved sol-gel method, in which tetrabutyl titanate (Ti(OC₄H₉)₄) and tetraethyl orthosilicate were chosen as the precursors and cobaltous nitrate hexahydrate (Co(NO₃)₂·6H₂O) was chosen as cobalt source. The field emission scanning electron microscopy and X-ray diffraction results indicated that the films were composed of nanoparticles or aggregates. The photoluminescence results revealed that the recombination rate of the photogenerated electrons and holes was prohibited via SiO₂ composite and Co doping in TiO₂ film. The Brunauer?CEmmett?CTeller results showed that the surface area of the modified TiO₂ was 301.7?m²?g^?1, while that of the pure TiO₂ was 68.4?m²?g^?1. The photocatalytic activities of the films were evaluated by degradation of an organic dye in aqueous solution. With the SiO₂ composite and Co doping, the modified TiO₂ films with high photocatalytic activity and clearly responsive to the visible light were obtained. The mechanisms of photoactivity enhancement for composite films have also been discussed.     

Synergistic Degradation of Eosin Y by Photocatalysis and Electrocatalysis in UV Irradiated Solution Containing Hybrid BiOCl/TiO2 Particles

The present work focused on treatment of eosin (EO) by photocatalysis (PC) combined with electrocatalysis (EC) process. Bismuth oxychloride/titanium dioxide (BiOCl/TiO₂) hybrid particles, which were used as new heterogeneous photocatalysts, were exploited in a reverse microemulsion approach and were characterized by XRD, UV?CVis diffuse spectra, BET, and SEM technologies. All degradation experiments were performed using a self-assemble experimental setup, in which PC and EC could be carried out simultaneously or individually. The results indicated that BiOCl/TiO₂ showed enhanced photocatalytic performance under UV irradiation, and 50% BiOCl/TiO₂ exhibited the best photoactivity due to its high degree of crystallization, the mesoporous structure and corresponding large special surface area, improved absorption ability in UV region, and the heterojunction formed between two coupling particles. The combined degradation process displayed synergistic effect on the degradation of EO owing to the generation of H₂O₂ at graphite cathode. The parameters such as, pH, reaction current, and initial concentration of EO were monitored in order to optimize the operating conditions. Pseudo-first-order kinetics was proposed and roughly fitted the combined degradation of EO. The combined system in this work suggested a new research idea for the degradation of dye wastewater.     

Speciation of Phosphorus and Cadmium in a Contaminated Soil Amended with Bone Char: Sequential Fractionations and XANES Spectroscopy

In this work, photocatalytic degradation of two reactive dyes, Reactive Yellow 84 (RY 84) and Reactive Black 5 (RB 5), on FeTiO₃/TiO₂ heterojunction in the presence of UV–visible radiation and H₂O₂ has been reported. FeTiO₃/TiO₂ heterojunction has been prepared from ilmenite FeTiO₃ and anatase TiO₂ by employing oxalic acid as an organic linker. FeTiO₃/TiO₂ ratios have been varied from 1 to 5 wt.%, and the materials were characterized by X-ray diffraction, scanning electron microscope and diffused reflectance UV–visible spectroscopic analysis. The photocatalytic activity of FeTiO₃/TiO₂ heterojunction for the degradation of the organic dyes RY 84 and RB 5 in the presence of UV–visible light was found to be higher than that of pure TiO₂. The addition of H₂O₂ increases the rate of degradation of both dyes on FeTiO₃/TiO₂ heterojunction. It facilitates the fast degradation of dye solutions even when their concentration was above 100 mg/l, which is otherwise very slow due to the low transmittance of light by the dye solution. The extent of mineralisation of the reactive dye during photocatalytic degradation was estimated from chemical oxygen demand analysis. FeTiO₃/TiO₂ heterojunction photocatalyst was also found to have good photostability; the material retains almost 97 % of its initial activity even in the fifth cycle.     

Photocatalytic Degradation of Reactive Black 5 by Fish Scale-Loaded TiO2 Composites

Titania and TiO₂/fish scale composites at different mass ratios (90:10, 70:30, and 50:50) were prepared by sol?Cgel method for application as photocatalysts in this study. Fish scale, synthesized TiO₂, and TiO₂/fish scale composites were characterized by using X-ray diffraction (XRD), scanning electron microscope (SEM), and nitrogen sorption. Their photocatalytic activities were evaluated through the degradation of Reactive Black 5 (RB 5) under solar light irradiation. The effects of irradiation time, catalyst loading, and mass ratios of TiO₂/fish scale composites on the photocatalytic degradation of RB 5 were investigated. The results revealed that the photocatalytic activity of TiO₂/fish scale composites showed compatible and enhanced degradation compared to the synthesized titania.     

Photodegradation of Bisphenol A with ZnO and TiO<Subscript>2</Subscript>: Influence of Metal Ions and Fenton Process

In this study, photocatalytic degradation of bisphenol A (BPA) was investigated using two types of catalysts (TiO₂ and ZnO) with various metal ion concentrations and amounts of added H₂O_2. A kinetic test was performed to observe the changes of BPA over time under UV irradiation in a photocatalytic reactor. Experimental results demonstrated that degradation efficiency of ZnO was higher than that of TiO₂. The degradation rate increased as catalyst dosage increased until reaching optimum dosage, after which degradation rate decreased. The addition of H₂O₂ improved the degradation efficiency of BPA, with the degradation efficiency increasing with the amount of H₂O₂. All metal ions, including Fe²⁺, Ni²⁺, and Cu²⁺, inhibited the degradation of BPA by ZnO at natural pH, whereas Fe²⁺ and Ni²⁺ enhanced degradation efficiency of BPA at acidic pH. Comparison of BPA degradation with H₂O₂ only, ZnO/H₂O₂, Fe²⁺/H₂O₂, and ZnO/Fe²⁺/H₂O₂ revealed that Fe²⁺/H₂O₂ was more efficient than other processes at lower pH (pH?=?3.44), whereas ZnO/H₂O₂ the most efficient at higher pH (pH?=?6.44). These results indicate that ZnO/H₂O₂ process was observed to be the most efficient of all processes. Degradation efficiency of BPA by ZnO was also influenced by additional parameters, including H₂O₂ concentration, metal ions, and solution pH.     

Quantitative mineralogy of bauxite profiles in se Guinea Bissau

In the South-Eastern part of Guinea Bissau extensive, highly weathered ferrallitic mantles occur within different geomorphological levels. These weathered layers are usually capped by petroplinthite. Frequently, they are of economic interest due to their enrichment in alumina. They represent the remnants of a Mezo-Cainozoic “African Planation Surface”. One hundred auger drill samples from one geomorphological structure—Bowal, were submitted to a specially developed method of quantification of the mineral phases previously detected in the representative specimens of the batch. The method consisted of computing the mineralogical composition from the principal chemical component analyses (Al₂O₃, SiO₂, Fe₂O₃, TiO₂, H₂O) combined with DTA/TG studies and thermodifferential X-ray diffraction studies. In addition, the samples from available core drillings, which reached the parent rocks, were investigated by means of XRD and optical microscopy. Two groups of bauxites developed on dolerite and shale yield the same mineral paragenese. The differences of mean Al₂O₃ and Fe₂O₃ content in both groups are expressed entirely by differences of concentration of gibbsite and goethite, which reflect mobility of aluminium and iron in solutions circulating through the system of open large pores. Boehmite and hematite would tend to crystallize from oversaturated solutions in confined environment of fine pores.     

Microstructures and Photocatalytic Properties of Fe3+/Ce3+ Codoped Nanocrystalline TiO2 Films

Fe³⁺ and Ce³⁺ codoped titanium dioxide films with high photocatalytic activity were successfully obtained via the improved sol?Cgel process. The as-prepared specimens were characterized using X-ray diffraction (XRD), high-resolution field emission scanning electron microscopy (FE-SEM), X-ray energy dispersive spectroscopy, Brunauer?CEmmett?CTeller (BET) surface area, X-ray photoelectron spectroscopy, photoluminescence (PL) spectra, and UV?CVis diffuse reflectance spectroscopy. The photocatalytic activities of the films were evaluated by degradation of various organic dyes in aqueous solutions. The results of XRD, FE-SEM, and BET analyses indicated that the TiO₂ film had nanostructure. With the codoping of Fe³⁺ and Ce³⁺, TiO₂ photocatalysts with smaller crystal size, larger surface area, and larger pore volume were obtained. Moreover, codoped ions could obviously not only suppress the formation of brookite phase but also inhibit the transformation of anatase to rutile at high temperature. Compared with pure TiO₂ film, Fe³⁺ doped or Ce³⁺ doped TiO₂ film, the Fe³⁺/Ce³⁺ codoped TiO₂ film exhibited excellent photocatalytic activity. It is believed that the surface microstructure of the films and the doping methods of the ions are responsible for improving the photocatalytic activity.     

Phytoremediation of Mixed Soil Contaminants

Tests were conducted to study the influence of non-ionic surfactants Triton X-100 and Tween 80 on the removal of mixed contaminants from a sandy soil using phytoremediation. Cd(II) and Pb(II) were used to form the inorganic contaminant, while used engine oil was selected to form the organic contaminant. The Indian mustard (Brassica juncea) plant was the plant chosen for phytoremediation of the sandy soil that contained the mixed contaminant. Thirty days after the plants were grown in the greenhouse, surfactants were applied to test pots in which the soil had been spiked with 50 mg kg⁻¹ of CdCl₂, 500 mg kg⁻¹ of PbCl₂ and 500 mg kg⁻¹ of used engine oil. Two control tests were conducted in this study. Planted and unplanted control tests were conducted using soil without surfactants. Following these tests, the tests were completed using the plants and surfactants at different concentrations. Test results showed that Triton X-100 and Tween 80 at concentrations higher than their critical micellar concentration enhanced Cd(II) and Pb(II) accumulation in the plant roots. Further, test data showed that translocation of contaminants to plant shoots occurred for Cd(II) but not for Pb(II). At the same concentrations, Tween 80 was more effective than Triton X-100 in facilitating rhizodegradation of used engine oil. This study demonstrates that simultaneous phytoremediation of Pb(II), Cd(II) and oil can be enhanced by using non-ionic surfactant Tween 80. Leaching test results indicated that the enhanced phytoremediation could remove the mixed contaminants safely from the point of view of limiting groundwater contamination.     

Mobilization of seed reserves pretreated with H2O2 during germination and establishment of sunflower seedlings under salinity

Abstract

Several studies have shown hydrogen peroxide (H₂O₂) as a metabolic messenger that increases plant tolerance to various stress conditions. However, little is known about its effect on the mobilization of seed reserves in the establishment of seedlings. Thus, this study aimed to evaluate the effect of pretreatment with H₂O₂ in salt-tolerance and mobilization of reserves during the germination of seeds and establishment of sunflower seedlings. Seeds were pre-imbibed for 24?hr in solutions containing: deionized water (control); H₂O₂ (1?mM); NaCl (100?mM). Subsequently, seeds were distributed on germitest paper, moistened with deionized water or saline solution (100?mM NaCl). In seedlings not pretreated with H₂O₂, the salinity increased Na⁺ and Cl^? ions contents and reduced the growth of sunflower seedlings. However, pretreatment of seeds with H₂O₂ reduced the negative effect of salinity, promoted an increase in salt-tolerance by the reduction of Na⁺ and Cl^? uptake, lower energy cost for osmoprotection by compatible solutes accumulation, and by the higher equilibrium in the mobilization of the cotyledon reserves for the development of the embryonic axis.     

The Oxidation of Di-(2-Ethylhexyl) Phthalate (DEHP) in Aqueous Solution by UV/H2O2 Photolysis

The oxidation of di-(2-ethylhexyl) phthalate (DEHP) in solution using UV/H₂O₂ and direct UV photolysis are analyzed in this study. It was found that DEHP was 100% removal in the solution by 180-min UV/H₂O₂ treatment and 73.5% removal by 180-min direct UV photolysis. The effect of different factors, such as DEHP concentration, H₂O₂ concentration, and UV light intensity, on photochemical degradation was investigated. The degradation mechanism of DEHP and the acute toxicity of intermediates were also studied. The photochemical degradation process was found to follow pseudo-first-order kinetics. The results of our study suggested that the concentration with 40 mg/L H₂O₂ and 5 μg/mL DEHP in the solution at pH 7 with 10.0?×?10^?6 Einstein l^?1?s^?1 UV was the optimal condition for the photochemical degradation of DEHP. The photochemical degradation with UV/H₂O₂ can be an efficient method to remove DEHP in wastewater.     

Degradation of Hazardous Dyes in Wastewater using Nanometer Mixed Crystal TiO2 Powders under Visible Light Irradiation

The partial phase transformation of nanometer TiO₂ powder from anatase phase to rutile phase was realized by heat-treatment and a new TiO₂ photocatalyst which could be excited by visible light was obtained. The heat-treated TiO₂ powder at different stage of transition crystal was characterized and monitored by XRD, TEM, FT-IR and UV–vis DRS methods. The test of photocatalytic activity of the heat-treated TiO₂ powder was carried out by the photocatalytic degradation of rhodamine B and acid orange II dyes, respectively, in aqueous solution under visible light irradiation. The results indicate that the nanometer TiO₂ photocatalyst heat-treated at 500°C for 60 min shows the highest photocatalytic activity, that is, it can effectively degrade the rhodamine B and acid orange II under visible light irradiation. The remarkable improvement of photocatalytic activity of heat-treated TiO₂ powder at 500°C for 60 min was mainly illustrated by the formation of special interphase between rutile and anatase phases, which not only restrains the recombination of photogenerated electrons and holes, but also reduces the adsorbability of nanometer anatase TiO₂ powder properly for various dyes. Additionally, the effects of dye-assisting chemicals such as Na₂CO₃ and NaCl on the photocatalytic degradation were also studied.     

Calcium accumulation alleviates soil acidification in Japanese cedar (Cryptomeria japonica) stands

Based on chemical and mechanical compositions and quartz content of red and/or yellow colored soil materials in the southwestern part of Japan, lithology index (LI) and weathering index (WI) were derived using a multivariate statistical method (factor analysis). The variables used for factor analysis are Fe₂O₃/Al₂O₃, TiO₂/Al₂O₃, Fe₂O₃+Al₂O₃+Quartz, Si(non-quartz)/(Fe₂O₃ + Al₂O₃), CaO + MgO + K₂O₃, MgO/K₂O₃ and Quartz/Sand, all of which represent certain different aspects of weathering and/or Iithological characteristics. Since LI and WI are mutually independent, it is possible to evaluate the effect of the degree of weathering on the characteristics of red and/or yellow colored soil materials independently from that of lithology.     

Comparative Studies on the Use of Binary and Ternary Combinations of Various Acidifying Agents for the Reduction of Soil pH

The present study deals with the effects of addition of sulfur along with other acidifying agents for their ability to lower and maintain the pH in a given range for a longer period of time. The chemicals were subjected to batch test individually and in combinations. Treatments were applied to three soils of different textures: sandy clay loam, clay loam, and silt loam. A 1:1 soil/water paste along with the added amendment was maintained at room temperature for 2 months. Most of the chemical treatments lowered the pH significantly. Combinations containing S/Al₂(SO₄)₃/H₂SO₄, S/Al₂(SO₄)₃/H₂O₂, and S/H₂O₂/H₂SO₄ were found to be very effective in lowering the pH. The soil pH remained acidic for 2 months, indicating the suitability of chemically amended soil for the plantations requiring acidic soil pH.     

钙对苹果果实超氧化物歧化酶、过氧化氢酶活性及其基因表达的影响

采用果实薄片培养试验研究不同钙浓度(0、1和10 mmo1/L CaCl2 ;5 mmo1/L EGTA)和处理时间(6、12、24和48 h)下苹果果实活性氧代谢特征;运用荧光定量PCR方法分析苹果超氧化物歧化酶（SOD）、过氧化氢酶（CAT）基因在分子水平的表达。高钙处理12 h后,SOD酶的活性显著增加,O2.-产生速率显著下降;高钙处理24 h后,CAT酶的活性显著增加,H2O2含量显著下降;缺钙处理下SOD酶和CAT酶的活性受到抑制,O2.-形成速率和H2O2含量显著增加。基因表达实验显示,高钙处理12h后,SOD基因的表达量增加,与SOD酶活性变化一致,说明SOD酶的活性取决于SOD基因的表达量;高钙处理12 h后,CAT1基因的表达量增加,而CAT酶的活性是在加钙处理24 h后显著增加,说明CAT酶的活性并不完全取决于CAT1基因的表达量,推断其酶活性还取决于该基因翻译后的修饰调控。上述研究表明苹果外源补钙通过在分子水平上调SOD和CAT1基因表达量来激活SOD和CAT酶的活性,有效减少体内活性氧积累,确保果实生理代谢平衡。     

Vertical Distribution of Trace Metals in Natural Soil Horizons from Japan Part 2: Effects of Organic Components in Soil

The association of Al, Mn, Fe, Ba, Zn, Cr, Ni, Co and Pb withsoil organic matter (SOM) was investigated in three Japanesesoils. Organically bound metals were assayed by elementalanalysis of a fraction extracted with acidified hydrogenperoxide (H₂O₂) and the humic acid extracted withalkaline reagent, from soil sampled at various depths of solums.A Dystric Cambisol showed higher extractability with acidifiedH₂O₂ for most of the metals than a Humic Andosol and an Orthic Acrisol. A Humic Andosol had more metals associated with humicacid than the other two soils.Cu showed high extractability with acidified H₂O₂ andalso significant association with humic acid, while Pb showedhigh extractability with acidified H₂O₂ but itsassociation with humic acid was relatively low among the metalsinvestigated. As humic acid is highly resistant to weathering,retention of Cu with SOM may last longer than that of Pb.The binding of metals with SOM probably has contributed to theaccumulation of some metals in organic-rich shallow horizons of soil. Such metals were Zn, Cu, Ni and Pb in a Dystric Cambisol,Cu in a Humic Andosol, and Pb and Cu in an Orthic Arisol.     

Reduction of N-Nitrosodimethylamine (NDMA) in Aqueous Solution by Nanoscale Fe/Al2(SO4)3

A novel immobilized visible light-active photocatalyst (TiO₂/polyvinyl alcohol after thermal treatment (T-PVA)/cordierite honeycomb (CHC)) was successfully prepared by a simple and convenient method combining sol–gel and thermal treatment using tetrabutyl titanate (TBOT) as the titanium source, polyvinyl alcohol (PVA) as the precursor of conjugated polymer, and CHC as the support. The synthesized photocatalyst was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ultraviolet–visible diffuse reflectance spectroscopy, and field emission scanning electron microscopy. The results showed that PVA was dehydrated to produce conjugated unsaturated T-PVA. The T-PVA not only extended the response spectrum of TiO₂ to visible light region, but also strengthened the adhesion of TiO₂ to CHC. The TiO₂/T-PVA/CHC showed both outstanding adsorption properties and excellent photocatalytic performance under visible light on the decolorization of Rhodamine B. Over eight cycles, the photocatalyst continued to maintain perfect photocatalytic activity, showing good stability.

Suitability of Two Methods for Determination of Point of Zero Charge (PZC) of Adsorbents in Soils

The points of zero charge (PZC) of manganese oxide (MnO₂), titanium dioxide (TiO₂), aluminum (Al) laterite, ferruginous (Fe) laterite, aluminum oxide (Al₂O₃), and a commercial activated carbon sample (AC001) were determined using acid-base potentiometric (PT) and mass titration (MT). The MT technique has been used extensively for carbonaceous materials but less for soils. In addition, little work has been done on the PZC of these metal oxides and carbon materials under similar experimental conditions concurrently. Our aim is to buttress the ease of MT usage over PT in routine laboratory analysis. The experimental PZC measured by acid-base potentiometric and mass titrations respectively were 4.97 and 4.11 for MnO₂; 5.38 and 5.74 for TiO₂; 4.19 and 4.08 for Al laterite; and 4.45 and 4.10 for Fe laterite. For Al₂O₃ and activated carbon, mass titration gave 7.53 and 8.41 respectively. Calculated standard deviations between the means of PT and MT were less than 1, and Student’s t-test at 95% confidence interval (CI) gave a P value of 0.135, suggesting that there is no significant difference between PT and MT and buttressing the reliability of the experimental procedures. In routine laboratory work, mass titration should be preferred for PZC measurement of (hydr)oxides and soil materials because it saves time.     

Trace elements in tropical Asian paddy soils

Attempts were made to evaluate correlations of total trace elements with various soil characters in the hope that such correlations would allow prediction of the trace element status of paddy soils in Tropical Asia.

Among the 11 trace elements studied, Ni and Cr showed by far the highest correlation, followed by the pairs of V and Zn, Ni and Zn, and Cr and Zn.

High positive correlations of trace elements with soil characters were found for the following pairs: total Fe₂O³, and V and Zn, total K₂0 and Rb, total CaO and Sr, total TiO₂, and V, total Al₂0³ and Zn, 10 Å clay content and Rb, clay and V, and sand and Zr. Among the negative correlations, the highest was between total SiO₂ and V, followed by those between total SiO₂ and Zn and sand and Zn.

Soil material classes and inherent potentiality ratings previously established were found to have some value for the prediction of the status of certain trace elements in soil.     

Equilibria of weak acids and organic Al complexes explain activity of H+ and Al3+ in a salt extract of exchangeable cations

Two sequential extractions with unbuffered 0.1 m BaCl₂ were done to study the release of salt-exchangeable H⁺ and Al from mineral horizons of five Podzols and a Cambisol. Released Al was found to have a charge close to 3+ in all horizons and in both extractions. This finding was supported by the near-equality of the titrated exchangeable acidity (EA_T) and the sum of exchangeable acids (EA = H_e + 3Al_e, calculated from the pH and Al concentration of the extract). The ratio between EA of the second and the first extraction was over 0.50 in the Bs2 and C horizons and smaller in the other horizons. H⁺ was assumed to be in equilibrium with weak acid groups, and the modified Henderson–Hasselbach equation, pK_HH = pH ? n log (α/(1 ? α)), was used to explain pH of the extract. The degree of dissociation (α) was calculated as the ratio between effective and potential cation exchange capacity. Value of the empirical constant n was found to be near unity in most horizons. When the monoprotic acid dissociation was assumed in all horizons, pK_HH had the same value in both extractions. For Al³⁺, two equilibrium models were evaluated, describing (i) complexation reactions of Al³⁺ with soil organic matter, and (ii) equilibrium with Al(OH)₃. Apparent equilibrium constants were written as (i) pK_o = xpH ? pAl³⁺, and (ii) log Q_gibbs= log Al³⁺ ? 3log H^+. The two extractions gave an average reaction stoichiometry x close to 2 in all horizons. Results suggest that an equilibrium with organic Al complexes can be used to express dissolved Al³⁺, aluminium being apparently bound to bidentate sites. The value of log Q_gibbs was below the solubility of gibbsite (log K_gibbs = 8.04) in many horizons. In addition, log Q_gibbs of the second extraction was greater than that of the first extraction in all horizons except the C horizon. This indicates that equilibrium with Al(OH)₃ cannot explain dissolved Al³⁺ in the soils. We propose that the models of pK_HH and pK_o can be used to simulate exchangeable H⁺ and Al³⁺ in soil acidification models.