Advanced approach for degradation of recalcitrant by nanophotocatalysis using nanocomposites and their future perspectives

Industrial effluents containing persistent pollutants play a significant role in environmental pollution. Classical techniques such as chlorination, coagulation, ion flotation, membrane process and sedimentation that have been used to decontaminate polluted water are incapable of efficient degradation due to the generation of secondary pollutants. Photocatalysis, an advanced oxidation process in which the photoreaction is accelerated by the irradiation of catalyst, has shown efficient degradation of recalcitrant in water system. Usage of nanoparticles as homogenous photocatalyst has become prevalent due to their improved properties such as large surface-to-volume ratio, controlled uniform particle size and its composition which enhances the degradation rate. The recombination of holes and electron pair which is considered to be the limitation in homogenous system can be overcome by nanocomposites or heterogeneous photocatalysts. This system decreases the rate of recombination, leading to effective degradation of individual pollutants because of their enhanced physicochemical and structural properties. In recent years, heterogeneous nanophotocatalytic processes employing titanium dioxide (TiO₂) and zinc oxide (ZnO) composites have gained immense research interest as an effective wastewater treatment method because of its efficacy in decomposing and mineralizing the hazardous organic and inorganic pollutants utilizing the UV and visible photons. This paper reviews about the process, synthesis and parameters influencing photocatalytic reaction and their kinetics with much emphasize on types of nanoparticles and nanocomposites and its application in wastewater treatment.     

Quantification of organic pollutant degradation in contaminated aquifers using compound specific stable isotope analysis - Review of recent developments

Compound specific stable isotope analysis (CSIA) has been established as a viable tool for proving, characterizing and assessing degradation of organic pollutants within contaminated aquifers. The fractionation of stable isotopes during contaminant degradation leads to observable shifts in stable isotope ratios which can serve as an indicator for in situ pollutant degradation and allow for a quantitative assessment by means of the so-called Rayleigh (distillation) equation.This review highlights the recent developments of the Rayleigh equation approach for quantifying in situ degradation of organic pollutants in contaminated aquifers. The advantages and limitations of the Rayleigh equation approach are discussed and suggestions for improvements are given. Concepts are provided to estimate the uncertainty due to errors or variability of input parameters and how to deal with such uncertainty. Moreover, the applicability of the Rayleigh equation approach is evaluated regarding the heterogeneity and complexity of groundwater systems. For such systems, the review discusses the relevance of non-destructive processes, which affect the concentration (e.g., dispersive mixing) and potentially also the stable isotope ratio of contaminants (e.g., sorption, volatilization), and the resulting implications for the Rayleigh equation approach.     

Quantification of organic pollutant degradation in contaminated aquifers using compound specific stable isotope analysis – Review of recent developments

Compound specific stable isotope analysis (CSIA) has been established as a viable tool for proving, characterizing and assessing degradation of organic pollutants within contaminated aquifers. The fractionation of stable isotopes during contaminant degradation leads to observable shifts in stable isotope ratios which can serve as an indicator for in situ pollutant degradation and allow for a quantitative assessment by means of the so-called Rayleigh (distillation) equation.This review highlights the recent developments of the Rayleigh equation approach for quantifying in situ degradation of organic pollutants in contaminated aquifers. The advantages and limitations of the Rayleigh equation approach are discussed and suggestions for improvements are given. Concepts are provided to estimate the uncertainty due to errors or variability of input parameters and how to deal with such uncertainty. Moreover, the applicability of the Rayleigh equation approach is evaluated regarding the heterogeneity and complexity of groundwater systems. For such systems, the review discusses the relevance of non-destructive processes, which affect the concentration (e.g., dispersive mixing) and potentially also the stable isotope ratio of contaminants (e.g., sorption, volatilization), and the resulting implications for the Rayleigh equation approach.     

Adsorption kinetics of herbicide paraquat in aqueous solution onto a low-cost adsorbent, swine-manure-derived biochar

Biochars have received increasing attention in recent years because of their significant properties such as carbon sequestration, soil fertility, and contaminant immobilization. In this work, the adsorptive removal of paraquat (1,1′-dimethyl-4,4′-dipyridinium chloride, one of the most widely used herbicides) from aqueous solution onto the swine-manure-derived biochar has been studied at 25 °C in a batch adsorption system. The adsorption rate has been investigated under the controlled process parameters including initial pH (i.e., 4.5, 6.0, 7.5, and 9.0), paraquat concentration (i.e., 0.5, 1.0, 2.0, 4.0, and 6.0 mg/L), and biochar dosage (i.e., 0.10, 0.15, 0.20, 0.25, and 0.30 g/L). Based on the adsorption affinity between cationic paraquat and carbon-like adsorbent, a pseudo-second order model has been developed using experimental data to predict the adsorption kinetic constant and equilibrium adsorption capacity. The results showed that the adsorption process could be satisfactorily described with the reaction model and were reasonably explained by assuming an adsorption mechanism in the ion exchange process. Overall, the results from this study demonstrated that the biomass-derived char can be used as a low-cost adsorbent for the removal of environmental cationic organic pollutants from the water environment.     

天然矿物材料的多孔结构、结构组装和光催化性能

自然界存在丰富的多孔矿物资源,其孔隙结构使其具有良好的吸附性能,能够吸附聚集水体中的污染物(特别是有机污染物)。在分析天然多孔矿物的孔结构基础上,文中提出了结构组装的概念,即在多孔矿物中进行功能粒子组装,对多孔矿物进行表面修饰、微结构组装(如层状结构矿物的插层)。通过结构组装,在多孔矿物中引进功能粒子(如有光催化性能的TiO2 颗粒)。组装在天然矿物中的功能粒子能够降解聚集在其中的污染物,大幅度提高功能粒子的效果,提高光催化降解的功效,获得性能优异、成本低廉的天然矿物型有机污染物降解材料。此外,在同一矿物材料中复合小孔、中孔、大孔不同大小的孔结构,实现不同大小的孔径组装,也能够扩大光催化剂TiO2 的承载面积,提高吸附性能。经过结构组装的天然多孔矿物材料复合了吸附、光催化等性能,在环境治理特别是有机物污染降解方面有很好的应用价值。     

Novel preparation of sensitized ZnS nanoparticles and its use in photocatalytic degradation of tetracycline

Sensitized ZnS nanoparticles were synthesized by chemical precipitation method using anthocyanin as the capping agent and sensitizer. X-ray diffractometer, field-emission scanning electron microscope, transmission electron microscopy, UV visible spectrophotometer, Fourier transform infrared spectroscopy and photoluminescence spectrometry methods were used for the characterization of nanoparticles. The electron microscopy studies of nanoparticles showed that the size of crystallites is in the range of 35–80 nm and optical studies showed a blue shift in the absorption edge by adding capping agent. The effective band gap energy was increased with decrease in the particle size. Photocatalytic activities of sensitized ZnS and pure ZnS were evaluated by degradation of tetracycline in aqueous solution under visible light irradiation, and progress of the reaction was monitored spectrophotometrically. The different parameters affecting degradation such as the pH of solution, amount of semiconductor and reusability of catalyst for three cycles and the photocatalytic degradation kinetics of tetracycline were studied. More than 80% degradation was achieved within 5 h under visible light.     

Fe/Ag催化臭氧氧化降解苯酚的研究

为研究双金属催化剂去除有机污染物的效果,采用自制Fe/Ag催化剂对模拟苯酚废水进行了臭氧催化氧化处理。通过扫描电子显微镜(SEM)、比表面积分析仪(BET)和X射线衍射(XRD)对催化剂进行表征,并考察了催化剂类型、催化剂投加量和溶液初始pH值对降解效果的影响规律。结果表明:与Fe相比,Fe/Ag比表面积减少了22.8%,在Fe/Ag/O₃与含苯酚废水的反应体系中,反应遵循臭氧直接作用和活性自由基(·OH、·O₂、H₂O₂)共同作用的机理;Fe/Ag在反应过程中体现出良好的协同作用;300 mg/L的苯酚模拟废水在pH=6.3、Fe/Ag投加量为1.00 g的最优反应条件下经60 min反应,苯酚与化学需氧量(COD)去除率比单独臭氧氧化分别提高了18.4%和29.4%。     

The phenomenon of deficient electron microprobe totals in radiation-damaged and altered zircon

The phenomenon of deficient electron microprobe analyses, with sums of analyzed constituents often below 95 wt%, is assigned to the analysis of altered, porous minerals. With the example of three zircon populations we show that low totals are related to textural features (i.e., numerous pores of tens to hundreds of nanometers size) as well as to the chemical composition (i.e., water content well within the wt% range, which may affect partial sample degradation under the electron beam). The formation of the spongy texture is explained by the alteration of a previously radiation-damaged and, thus, volume-expanded material in a fluid-driven replacement reaction. The smaller volume of the reaction product (crystalline, non volume-expanded zircon) accounts for the formation of numerous voids and pores, which are perfect candidates for the incorporation of water. The alteration has also resulted in uptake of non-formula elements such as Al, P, Ca, Fe, Y, and REEs whereas Si and Zr are depleted. In one case, strong uptake of non-radiogenic Pb in altered zircon was observed. Because porous, low-total zircon has formed in secondary alteration process, its occurrence can be considered as an indicator of a secondary alteration history of the host rock. Low-total zircon is easily recognized by very low electron back-scatter intensities, which are closely related to the two main causes of the analytical shortfall (i.e., water content and porosity) and often lowered furthermore by the presence of light non-formula elements (especially P and Fe) up to the wt% range.     

生态水文学:生态需水及其与流速因素的相互作用

本文研究涉及生态水文学中生态需水问题的一般认知。探讨了生态系统动态变化与水流驱动力因素之间的关系，重点探讨水流驱动因素中的关键指标—流速，通过分析流速与生态系统相互作用，从生态水文学动力因素出发估算生态需水；基于生态流速和水力半径，提出考虑河道内生态需水与水力因素关系的生态水力半径法，充分利用水生生物信息（鱼类产卵洄游流速）与河道信息（水位、流速、糙率等）估算河道内生态需水；归纳生态水力半径法在生态需水计算中的初步应用:考虑污染物降解耦合水量水质的生态需水计算、考虑鱼类等生物对流速要求的生态需水计算、考虑河道冲淤平衡的输沙需水量计算等方面。本文提出的生态流速研究既包括生物生长发育适宜的流速，又包括流速大小变化所涉及的许多动力因素，旨在延伸与扩展生态水文学的内涵与应用。     

生态水文学:生态需水及其与流速因素的相互作用

本文研究涉及生态水文学中生态需水问题的一般认知。探讨了生态系统动态变化与水流驱动力因素之间的关系，重点探讨水流驱动因素中的关键指标——流速，通过分析流速与生态系统相互作用，从生态水文学动力因素出发估算生态需水；基于生态流速和水力半径，提出考虑河道内生态需水与水力因素关系的生态水力半径法，充分利用水生生物信息（鱼类产卵洄游流速）与河道信息（水位、流速、糙率等）估算河道内生态需水；归纳生态水力半径法在生态需水计算中的初步应用：考虑污染物降解耦合水量水质的生态需水计算、考虑鱼类等生物对流速要求的生态需水计算、考虑河道冲淤平衡的输沙需水量计算等方面。本文提出的生态流速研究既包括生物生长发育适宜的流速，又包括流速大小变化所涉及的许多动力因素，旨在延伸与扩展生态水文学的内涵与应用。     

Photocatalytic degradation of azo dye Orange II in aqueous solutions using copper-impregnated titania

During dyeing process, industries consume large quantity of water and subsequently produce large volume of wastewater. This wastewater is rich in color and contains different dyes. Orange II is one of them. In this article, metal-impregnated TiO₂ P-25 catalyst was used to enhance the photocatalytic degradation of Orange II dye. Photodegradation percentage was followed spectrophotometrically by the measurements of absorbance at λ _max = 483 nm. The effect of copper-impregnated TiO₂ P-25 photocatalyst for the degradation of Orange II has been investigated in terms of percentage removal of color, chemical oxygen demand (COD) and total organic carbon (TOC). As such 98 % color removal efficiency, 97 % percentage removal of COD and 89 % percentage removal of TOC was achieved with TiO₂ P-25/Cu catalysts under typical conditions. Copper-impregnated TiO₂ P-25 photocatalyst showed comparatively higher activity than UV/H₂O₂ homogeneous photodegradation. The relative electrical energy consumption for photocatalytic degradation was considerably lower with TiO₂ P-25/Cu photocatalyst than that with homogeneous photodegradation. Transmission electron microscopic analysis was used for catalyst characterization.     

Fate and biodegradability potential of an emerging micropollutant diclofenac in subsurface environment

The present study deals with the assessment of the fate of an emerging contaminant (diclofenac), present in the subsurface environment at specific concentration levels, and its biodegradation potential under different environmental configurations. Diclofenac is a widely consumed nonsteroidal anti-inflammatory drug used as a painkiller prescribed as pills or ointments and among the most frequently detected pharmaceuticals in wastewater treatment plants’ effluents. Fermentative/methanogenic cultures were enriched from previously contaminated sediment samples. Although partial biodegradation was achieved in all enrichment cultures, complete degradation was not observed. The results reflected that less than 6% of the diclofenac sorbed on the solid phase and the rest was either biotransformed (25–40%) or remained in the liquid phase (55–70%) at the end of 45-day incubation period. Although partial cometabolic degradation of diclofenac occurred in the presence of glucose, biodegradation was not observed in the presence of readily biodegradable carbon source (i.e., acetate). Diclofenac concentration up to 1000 µg/L did not affect the methanogenic activity of the enriched culture. The results of this study will have a significant impact in the designation of the permitted concentration limits of diclofenac before the discharge through wastewater treatment plants.     

基于SEM-EDS及GC-MS技术研究有机氯分子结构对零价铜脱氯机制的影响

零价铜作为一种廉价金属很少应用于促进氯代有机物脱氯研究,其原因是零价铜的催化还原脱氯活性差,且反应机制复杂。本文采用机械球磨技术制备了Cu-Fe和Cu-Ni合金,研究零价铜在不同微观环境下对对氯苯酚(4-CP)的脱氯行为,旨在考察有机氯分子结构对零价铜脱氯机制的影响。应用扫描电镜-能谱(SEM-EDS)及色相色谱-质谱(GC-MS)分析发现,铜原子的微环境及有机氯分子结构均影响铜的脱氯机制。在Cu-Fe体系中,Cu遵循经典的催化加氢脱氯机制,4-CP的降解产物为苯酚;Cu-Ni体系的还原作用来源于零价铜,其中的镍金属并未起到催化加氢作用,Cu-Ni合金及单独零价铜对4-CP的降解产物是环己酮。零价铜对4-CP的降解率可达70%以上,而Cu-Fe体系的降解率仅为34%,两者对芳香族氯代物的降解效率差距显著。零价铜能够降解化学稳定性高的4-CP和苯酚,但不能降解化学稳定性相对较差的脂肪族氯代有机物(如一氯乙酸和二氯乙酸),因此认为零价铜脱氯机制并非传统的催化加氢机制,而是遵循直接电子传递还原机制,且有机氯分子的苯环结构是零价铜直接电子传递还原的诱因。     

微生物所协同的天然金红石日光催化作用研究

本文揭示了自然界中可能存在的一种新的矿物和微生物交互作用形式,即微生物通过生物电化学作用参与到半导体 矿物的日光催化作用过程中。模拟日光光源下“产电”微生物与天然半导体矿物金红石交互实验结果显示,金红石的光催 化作用促进了矿物端元的反应速率,提高了电子在微生物和矿物之间的转移效率,使微生物电子传递链末端电子能量得到 提升。二者协同作用可提高微生物或半导体矿物单独作用时对污染物如Cr(Ⅵ)的还原处理效果。该研究为环境污染治理提 供了一种矿物与微生物协同作用新理念。     

Photocatalytic treatment of oil and grease spills in wastewater using coated N-doped TiO<Subscript>2</Subscript> polyscales under sunlight as an alternative driving energy

To enhance the overall efficiency of oil and grease removal in wastewater coated N-doped TiO₂ photocatalytic polyscales were fabricated through sol–gel technique. The materials fabricated were characterized using powder X-ray diffraction, Fourier transmission infrared spectroscopy, scanning electron microscopy, and UV–Vis spectroscopy. In order to enhance degradation efficiency of organic pollutant under natural sun light, shifting of absorption range of TiO₂ to visible spectrum, various modifications such as surface modification and size optimization were carried out by doping of nitrogen under sol–gel processes. To ease recovery of suspended catalysts from aqueous media, the coated N-doped TiO₂ were prepared by decorating photocatalytic particles onto suitable substrates. N-doped TiO₂ polyscales with desired functionalities were coated onto the spherical supporting substrates using a binding agent. The photocatalytic treatment studies clearly indicated the considerable level of the oil and grease and other organic pollutants removal from wastewater (up to 85–90 % ± 2) using coated N-doped TiO₂ under natural sunlight as an alternative driving energy source. Removal of oil and grease along with other organic pollutants in wastewater using coated N-doped TiO₂ polyscales is a versatile, economical, and environmental friendly technique due to the ease of handling and recovery, utilization of natural sunlight which is renewable energy source.     

Vertical migration of municipal wastewater in deep injection well systems,South Florida,USA

Deep well injection is widely used in South Florida, USA for wastewater disposal largely because of the presence of an injection zone (“boulder zone” of Floridan Aquifer System) that is capable of accepting very large quantities of fluids, in some wells over 75,000 m³/day. The greatest potential risk to public health associated with deep injection wells in South Florida is vertical migration of wastewater, containing pathogenic microorganisms and pollutants, into brackish-water aquifer zones that are being used for alternative water-supply projects such as aquifer storage and recovery. Upwards migration of municipal wastewater has occurred in a minority of South Florida injection systems. The results of solute-transport modeling using the SEAWAT program indicate that the measured vertical hydraulic conductivities of the rock matrix would allow for only minimal vertical migration. Fracturing at some sites increased the equivalent average vertical hydraulic conductivity of confining zone strata by approximately four orders of magnitude and allowed for vertical migration rates of up 80 m/year. Even where vertical migration was rapid, the documented transit times are likely long enough for the inactivation of pathogenic microorganisms.     

Response surface methodology (RSM) optimization approach for degradation of Direct Blue 71 dye using CuO–ZnO nanocomposite

The present study highlights the synthesis of CuO–ZnO nanocomposite via facile hydrothermal method at 150 °C and autogenous pressure. The structural and textural features of prepared composite material was characterized by several characterization techniques such as X-ray powder diffraction, Fourier transform infrared spectroscopy, Scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The optimized prepared nanocomposite was utilized for photocatalytic degradation of aromatic Direct Blue 71 dye (DB71) under natural sunlight conditions. The catalytic activity results by CuO–ZnO nanocomposite were observed to be higher than the reagent-grade zinc oxide under visible light conditions. The response surface methodology protocol (RSM) with central composite design was optimized by different photodegradation operational parameters such as pH, dye concentration, catalyst amount, and reaction time. The optimized RSM results demonstrated that a quadratic polynomial model was found suitable to define the relation between the photocatalytic activity and operational parameters. Moreover, the observed high R ² value (0.9786) confirms a strong evaluation of experimental data. To achieve maximum DB71 degradation, optimized condition was found at 177.13 min of contact time, 3.93 solution pH, and 24.34 mg/L of dye concentration with 1.85 g/L of catalyst dose The identical optimum conditions resulted maximum 89.58% DB71 degradation.     

Mineralogical features and genesis of Polyanskoye mercury deposit on Chukotka

The mineralogy of two gold deposits in southwestern China, which contain gold entirely in the form of microscopic or submicroscopic grains or inclusions, is examined. They contain refractory or low-grade ores similar in type to those near Carlin, Nevada. Mineralogical studies of ore samples from the two deposits (e.g., proton microprobe analysis, scanning electron microscope analysis, electron microprobe analysis, X-ray diffraction studies, ore microscopy) indicate that the predominant gold-bearing minerals are pyrite (Dongbeizhai deposit) and arsenopyrite and pyrite (Jinya deposit). Gold in the two deposits is closely correlated with As, S., and Fe.     

Decomposition of multi-class pharmaceutical residues in wastewater by exposure to ionising radiation

This paper reports an experimental degradation study of nineteen multi-class pharmaceutical products present in the influent wastewater arriving at the Daugavgriva wastewater treatment plant. Collected wastewater samples were filtered and irradiated by electron beam and gamma radiation both generated from a 5 MeV linear particle accelerator. The samples were exposed to ten absorbed doses (0.5–25 kGy) produced at high dose rates (600 and 1200 kGy h^?1 for accelerated electrons, as well as 22.5 and 37.5 kGy h^?1 for gamma radiation). The analysis by a sensitive liquid chromatography–mass spectrometry method indicated that the initial concentrations of pharmaceutical residues were effectively reduced by up to 90–100% in eighty per cent of the cases when samples were exposed to 0.5–5 kGy of electron beam or gamma radiation treatment. Higher doses (>5 kGy) were needed to decompose macrolide antibiotics. The use of electron beam radiation showed some advantages due to the reduced exposure time, thus enabling a more energy efficient treatment resulting in the degradation of pharmaceutical residues comparable to that achieved by gamma irradiation. Microbiological studies indicated the pronounced degradation effect on bacterial contamination of wastewater, which was successfully eliminated upon increasing the radiation, dose up to 7–12 kGy.     

Fe2O3-TiO2复合光催化剂的制备及其对染料酸性大红降解的光催化活性研究

以氧化铁红粉末为载体,钛酸四丁酯为前驱体,无水乙醇为溶剂,制备了Fe2O3-TiO2光催化剂。用XRD、TEM等对催化剂的物相、形貌进行了表征,并通过对酸性大红GR染料废水进行光催化降解实验,研究了催化剂的投加量、光照时间以及起始浓度、pH值、回收方法及催化剂重复使用次数对酸性大红染料废水光降解作用的影响。实验结果表明,氧化铁红粉末负载TiO2催化剂有很好的吸附和光催化性能,并可以多次回收重复使用,在投加量为0.4g/L的条件下,光催化效果最好,1h后的脱色率可达95%以上。