Fabrication of binary metal doped CuO nanocatalyst and their application for the industrial effluents treatment

Herein, we fabricated the binary transition metal (Ce & Zn) doped CuO nanocatalyst via a single step facile co-precipitation technique by using liquid ammonia as a pH regulator and precipitating agent. The structural, morphological, and compositional studies of the fabricated samples were completed via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and EDX techniques, respectively. The impact of binary metal-doped CuO nanocatalyst on the optical band-gap was examined via the UV-Visible spectroscopic technique. The photocatalytic aptitude of the fabricated pristine and binary metal-doped CuO nanocatalyst was examined against the 5-ppm aqueous solution of MB dye. The obtained results revealed that the doped sample removes 81.64% MB dye, via adsorption (32.65%) and degradation (48.99%) processes, while in comparison the pristine CuO sample removes just 38.77%. The superior adsorption and degradation aptitude of the binary metal-doped sample can be ascribed to its higher surface area and tuned band-gap, respectively. Moreover, the kinetic study of the degradation process also displayed that the doped sample degrades the MB dye with a higher value of the rate constant (0.0137 min^?1) than that of pristine CuO photocatalyst (0.0049 min^?1). The tuned band-gap and nanoarchitecture morphology of the doped CuO not only facilitate the excitation process but also assist in the transportation of the photo-induced species towards the surface of the photocatalyst. The observed superior photocatalytic activity of the binary metal-doped CuO photocatalyst showed its exceptional aptitude for the treatment of toxic industrial effluents.     

Synthesis of La1-xGdxFe1-yCoyO3/r-GO nanocomposite with integrated features for the treatment of hazardous industrial effluents

Solar-light triggered semiconductive materials with a small bandgap, a low electron-hole pair recombination rate, and quicker charge carrier characteristics are very efficient catalysts for hazardous industrial effluent treatment. Herein, we adopted wet-chemical and ultra-sonication techniques to prepare binary metal (Gd & Co) doped Lanthanum ferrite (GCLFO) nanoparticles and their reduced-graphene (r-GO) based nanocomposite (GCLFO/r-GO) as an ideal photocatalyst. The binary metal doping and composite formation strategies were adopted primarily to facilitate the electronic excitation and accelerate the charge transport characteristics of the finally obtained photocatalyst. Prepared solid samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman, Fourier transform-infrared (FT-IR), current-voltage (I–V), BET (Brunauer, Emmett, and Teller), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. An improvement in the photo-degradation of Phenol Red (PR) dye by GCLFO/r-GO nanocomposite was observed. The increased photocatalytic activity of the GCLFO/r-GO nanocomposite is primarily a result of doping, nanotechnology, and composite formation strategies. These strategies tune the bandgap of the nanocomposite sample, increase its surface area, and decrease its electrical resistivity. Highly encouraging photocatalytic findings suggest that using multiple strategies to prepare an ideal photocatalytic material with integrated features is a very efficient approach.     

Facile synthesis of CdS nanoparticles photocatalyst with high performance

A simple one-step solid-state reaction has been introduced to synthesize CdS nanoparticles. The as-prepared CdS product was characterized by X-ray powder diffraction (XRD), BET surface area measurement, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), particle size distribution (PSD) and UV–vis absorption spectrum. The experiment results reveal that the CdS product was composed of nanoparticles about 60 nm in diameter, of which specific surface area is 78.02 m²/g. The photocatalysis results indicate that the CdS nanoparticles exhibit excellent photocatalytic activity for the degradation of rhodamine B under UV irradiation. Nearly 95% of rhodamine B was degraded after 60 min of irradiation, higher than that of P25, which is due to the large specific surface area and mesoporous structure.     

Sol-gel synthesis of new TiO2/activated carbon photocatalyst and its application for degradation of tetracycline

A new efficient photocatalyst consisting of TiO₂-activated carbon composite (TiO₂/AC) was synthesized by sol-gel process and applied to decomposition of tetracycline (TC). Its properties and catalytic activity were evaluated in comparison with bare TiO₂ and P25, based on several characterization techniques and TC photodegradation kinetic studies. The results showed TiO₂/AC has better structural and electronic features for photocatalysis; S_BET of 129 m² g^–1, exclusively anatase phase, crystal size of 8.53 nm and band gap energy of 3.04 eV. The catalytic activity of the material was evaluated based on photodegradation kinetic studies of TC from aqueous solution (with initial concentration=50 mg L⁻¹ and catalyst dosage=1.0 g L⁻¹). Non-linear kinetic model of pseudo-first order were fitted to the resulting experimental data. The apparent first-order rate constant (k_app=42.9×10^–3 min^–1) and half-life time (t_1/2=16.1 min) determined for TiO₂/AC were better than those for P25 and bare TiO₂. TC degradation by-products were investigated by HPLC-MS, showing TC was completely degraded after 75 min, producing fragments with m/z smaller than 150.     

Facile solvothermal synthesis of cube-like Ag@AgCl: a highly efficient visible light photocatalyst

In this paper, a stable and highly efficient plasmonic photocatalyst, Ag@AgCl, with cube-like morphology, has been successfully prepared via a simple hydrothermal method. Using methylene dichloride as chlorine source in the synthesis can efficiently control the morphology of Ag@AgCl, due to the low release rate of chloride ions. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectra were used to characterize the obtained product. The photocatalytic activity of the obtained product was evaluated by the photodegradation of methyl orange (MO) under visible light irradiation, and it was found, interestingly, that Ag@AgCl exhibits high visible light photocatalytic activity and good stability.     

Facile synthesis of micro-spherical LiMn0.7Fe0.3PO4/C cathodes with advanced cycle life and rate performance for lithium-ion battery

A series of micro-spherical LiMn_0.7Fe_0.3PO₄/C (LMFP) cathode materials are synthesized via co-precipitation method combining spray drying and solid-state reaction. All as-prepared materials are well-characterized to determine their crystal structure, morphology and electrochemical performance. All as-obtained LMFP materials correspond to orthorhombic olivine structure with Pbnm space group and show uniform porous spherical structure with an average particle size of 3 µm and a carbon coating layer of about 3 nm. In particular, the resulting LMFP material prepared at 600 °C exhibits a high discharge capacity of 160 mAh g⁻¹ at 0.1 C. Even at a high rate of 10 C, it can still deliver 133 mAh g⁻¹ and maintain capacity retention of 84.9% after 200 cycles. The excellent electrochemical performance is ascribed to the synergetic effect of porous micro-spherical structure and uniform carbon coating layer.     

The treatment of industrial effluents with high salinity and organic contents

Particularly problematic industrial effluents are those which contain high concentrations of both inorganic salts and organics. Some advanced technologies with their limitations are described.A few examples of the application of some membrane processes are given to demonstrate their potential use in the treatment of effluents from industries such as maize starch milling, tanneries, both sulphite and soda pulp mills, and a cotton textile factory.     

Continuous operation of membrane processes for the treatment of industrial effluents

The feasibility of operating a Non-Dispersive Solvent Extraction (NDSX) process in a continuous mode is analysed for the first time in this work. A configuration is proposed for the treatment of industrial effluents and metal recovery. The pollutant is removed from the effluent in the extraction module and simultaneously it is recovered in the stripping module, for recycling and re-use in the plant that generates the effluent. Thus, the amount of pollutant disposed of into the environment is reduced. The optimum membrane areas and the operating conditions are calculated solving a non-linear programming problem that includes the differential equations representing the composition profiles in the membrane modules. A particular application of this technology is evaluated, to remove Cr(VI) from surface treatment effluents, recover and concentrate it for recycle and reuse. The optimum operating conditions and areas of the extraction and stripping membranes, calculated at different Cr(VI) effluent compositions, are reported.     

臭氧催化氧化在工业废水处理中的应用进展

臭氧催化氧化因O₃分子的强氧化性和催化协同产生羟基自由基的二次氧化性,使其广泛应用于难降解工业废水处理工艺中。回顾了臭氧催化氧化在工业废水预处理以及深度处理单元中的研究应用,指出了现阶段臭氧催化氧化中存在的臭氧利用率低、生产成本高、金属离子溶出等问题,对提高臭氧利用率、催化剂评价体系和结合反应机理探索不同类型工业废水高效催化剂等三方面提出了展望。     

Fundamentals of electrosorption on activated carbon for wastewater treatment of industrial effluents

The potential of electroadsorption/desorption on activated carbon for waste water treatment of industrial effluents is studied. Adsorption isotherms of hydrophobic differently charged model substances on activated carbon were measured in order to obtain specific information about the influence of the charge (+1,–1 and 0) on the adsorbability of comparable, aromatic species and the influence of the bed potential on the adsorption equilibria. In all these cases the adsorption equilibria show a dependence on applied potential in electrolyte of approximately 1m ionic strength. With electrosorption from aqueous solution, a fivefold enhancement of the concentration in one potential controlled adsorption/desorption cycle is achievable. The use of the solvent methanol instead of water for desorption allows for a concentration enhancement by a factor of hundred in the desorptive step. The adsorption capacity of the activated carbon changes only slightly with cycle number. Two cell designs for the performance of potential controlled adsorption/desorption cycles on the large scale are discussed.     

Facile synthesis of Ag/AgBr/RGO nanocomposite as a highly efficient sunlight plasmonic photocatalyst

Well-dispersed Ag/AgBr colloidal spheres and the corresponding reduced graphene oxide (RGO) hybridized nanocomposite, Ag/AgBr/RGO, were synthesized by a simple one-step polyolthermal method. By rational tuning the synthesis conditions such as the content of polyvinylpyrrolidone (PVP), hexadecyltrimethyl ammonium bromide (CTAB), and the initial reaction temperature, the morphology, size and dispersity of the Ag/AgBr products can be easily controlled. The formation mechanism of as-prepared Ag/AgBr colloidal spheres was further proposed. The hybridization of Ag/AgBr spheres with RGO enhanced the composite catalytic performance, and the Ag/AgBr/RGO hybrid exhibited excellent catalytic activity and stability towards decomposition of Rhodamine B (RhB) under sunlight irradiation.     

Spiral-wound membrane reverse osmosis and the treatment of industrial effluents

Reverse osmosis (RO) is increasingly used as a separation technique in chemical and environmental engineering where desalination, selective separation and wastewater treatment are well established examples. Treatment by RO reduces high levels of dissolved salts but has certain limitations when used for the removal of organic compounds from effluents of the chemical industry. The spiral-wound membrane element is the most widely used membrane device because it has a high membrane surface area to volume ratio, it is easy to replace and can be manufactured from a wide variety of materials. This work forms part of a wider research project aimed at recovering products and reducing the concentration of pollutants in wastewater by using membrane process. The synthetic effluent stream that was treated contained an organic product (acrylnitrile) and four inorganic species (sulphate, ammonium, cyanide and sodium). It was found that the pH value ofthe solution plays an important role in the ionization of the different species and, subsequently, in their retention. The object of this study was to reduce the concentration of pollutants to the levels of mentioned regulations concerning discharges, using a pilot plant with a spiral-wound membrane element (0.56 m² surface area) and a polyamide membrane, which was previously selected. The RO measurements were carried out in a closed-loop controlled-pressure system, with the solution being constantly fed through the spiral-wound membrane. The rejection percentage of sulphate ion was high in the two treatments assayed, regardless ofthe operational pH and sequence of steps followed. The degree to which NH₄⁺ and CN⁻ were eliminated was strongly dependent on the pH of the feed stream. Ammonium ion, too, was strongly eliminated regardless ofthe sequence ofthe steps, while the best results with CN⁻ were obtained when the first step had a nearly neutral pH and the second a pH of 11.0. Acrylnitrile showed low rejection percentages in all the steps carried out.     

A novel approach for the synthesis of highly active ZnO/TiO2/Ag2O nanocomposite and its photocatalytic applications

The present work is focused on the preparation of hybrid ZnO/TiO₂/Ag₂O nanocomposite for enhanced photocatalytic activity. The resultant samples are characterized by using XRD, SEM, EDX, HR-TEM, UV-DRS, BET and XPS techniques. X-ray diffraction analysis indicates the co-existence of wurtzite, anatase and cubic phases in ZnO/TiO₂/Ag₂O nanocomposite. The band gap energy value of the photocatalyst is 3.39 eV, which has been evidenced from UV–visible diffuse reflectance spectroscopy measurements. Photocatalytic degradation of methylene blue dye has been investigated by using UV–visible spectrophotometer. From the result, it has been concluded that ZnO/TiO₂/Ag₂O nanocomposite has proven to be an efficient photocatalyst under UV irradiation when compared to that of mono and binary oxide systems. Further, the possible photodegradation mechanism is proposed to support the enhancement of photocatalytic activity towards degradation of dyes.     

Facile synthesis and electrochemical performances of hollow graphene spheres as anode material for lithium-ion batteries

The hollow graphene oxide spheres have been successfully fabricated from graphene oxide nanosheets utilizing a water-in-oil emulsion technique, which were prepared from natural flake graphite by oxidation and ultrasonic treatment. The hollow graphene oxide spheres were reduced to hollow graphene spheres at 500°C for 3 h under an atmosphere of Ar(95%)/H₂(5%). The first reversible specific capacity of the hollow graphene spheres was as high as 903 mAh g^-1 at a current density of 50 mAh g^-1. Even at a high current density of 500 mAh g^-1, the reversible specific capacity remained at 502 mAh g^-1. After 60 cycles, the reversible capacity was still kept at 652 mAh g^-1 at the current density of 50 mAh g^-1. These results indicate that the prepared hollow graphene spheres possess excellent electrochemical performances for lithium storage. The high rate performance of hollow graphene spheres thanks to the hollow structure, thin and porous shells consisting of graphene sheets.

PACS

81.05.ue; 61.48.Gh; 72.80.Vp     

Facile synthesis and strongly microstructure-dependent electrochemical properties of graphene/manganese dioxide composites for supercapacitors

Graphene has attracted much attention since it was firstly stripped from graphite by two physicists in 2004, and the supercapacitor based on graphene has obtained wide attention and much investment as well. For practical applications of graphene-based supercapacitors, however, there are still many challenges to solve, for instance, to simplify the technological process, to lower the fabrication cost, and to improve the electrochemical performance. In this work, graphene/MnO₂ composites are prepared by a microwave sintering method, and we report here a relatively simple method for the supercapacitor packaging, i.e., dipping Ni-foam into a graphene/MnO₂ composite solution directly for a period of time to coat the active material on a current collector. It is found that the microwave reaction time has a significant effect on the microstructure of graphene/MnO₂ composites, and consequently, the electrochemical properties of the supercapacitors based on graphene/MnO₂ composites are strongly microstructure dependent. An appropriately longer microwave reaction time, namely, 15 min, facilitates a very dense and homogeneous microstructure of the graphene/MnO₂ composites, and thus, excellent electrochemical performance is achieved in the supercapacitor device, including a high specific capacitance of 296 F/g and a high capacitance retention of 93% after 3,000 times of charging/discharging cycles.

PACS

81.05.ue; 78.67.Sc; 88.80.fh     

Facile synthesis of silicon dioxide nanoparticles decorated multi-walled carbon nanotubes with graphitization and carboxylation for electrochemical detection of gallic acid

We proposed an efficient and scalable ultrasound-assisted approach for the synthesis of functionally integrated nanohybrid of silicon dioxide (SiO₂) nanoparticles and multi-walled carbon nanotubes with graphitization and carboxylation (GCMCN), which was employed to modify the glassy carbon electrode (GCE) for the fabrication of GCMCN@SiO₂/GCE sensor. Graphitization of GCMCN contributed to the reduction of defect density and enhancement of electrical conductivity, and carboxylation of GCMCN improved the dispersion degree of carbon nanomaterial due to the hydrophilicity of carboxyl groups. SiO₂ nanoparticles possessed abundant binding active sites for target analytes due to the surface hydroxyl groups or silanol groups, which were beneficial for the enrichment of gallic acid (GA) molecules. For the functionally integrated GCMCN@SiO₂ nanocomposite, the interconnected conductive networks of GCMCN presented more efficient charge transport channels, which recompensed the non-conductive property of SiO₂ nanoparticles. Based on the functional collaboration of GCMCN and SiO₂ nanoparticles, the fabricated GCMCN@SiO₂/GCE sensor presented good GA detection property (GA concentration: 0.01–15 μM, LOD value: 1.99 nM). The proposed sensor exhibited acceptable repeatability, reproducibility, and selectivity. Moreover, the good practicability performance could be effectuated at the GCMCN@SiO₂/GCE sensor for the quantitative analysis of GA in black tea and green tea samples.     

Co-precipitation synthesis and two-step sintering of YAG powders for transparent ceramics

Yttrium aluminum garnet (Y₃Al₅O₁₂, YAG) precursor was synthesized by the co-precipitation method with ammonium hydrogen carbonate as the precipitant. The influence of aging and calcination temperature on the precursor composition and transformation temperature of the YAG phase was investigated. On that basis, a two-step sintering (TSS) method (heating the sample up to 1800 °C followed by holding it at 1600 °C for 8 h) was used to fabricate bulk transparent YAG ceramics in vacuum (10⁻³ Pa) in this communication. A variety of techniques, such as X-ray powder diffraction, infrared spectra, scanning electron microscopy and UV–vis–NIR spectrophotometry were adopted to characterize the resulting YAG powders and ceramics. The results showed that aging had a dramatic effect on the precursor composition, which in turn influenced the transformation temperature of the YAG phase. Loosely agglomerated YAG powders with a mean particle size of 50 nm were obtained by calcinating the precursor without aging at 1000 °C. Finally, a transparent YAG ceramic specimen, achieving the in-line transmittance of 41% in the visible wavelength region and a nearly pore-free microstructure with uniform grains of about 4 μm, was produced via the TSS technique.     

Electrochemical synthesis of a novel poly(2,5-dimethoxy aniline) nanorod for ultrasensitive glucose biosensor application

We report for the first time a rapid electrochemical synthesis of one-dimensional poly(2,5-dimethoxyaniline) nanorods (PDMA-NR) in the presence of surfactant. FE-SEM and TEM images confirm the PDMA-NR formation and the average diameter of single rod sizes in the range of ∼200–300 nm. An enzymatic glucose biosensor was fabricated through immobilizing glucose oxidase (GOx) into PDMA-NR matrix. The amperometric current response of PDMA-NR/GOx to glucose is linear in the concentration range between 1 and 10 μM with a detection limit of 0.5 μM (S/N = 3). The PDMA-NR/GOx electrode possesses high sensitivity (5.03 μA/μM), selectivity, stability, and reproducibility toward glucose.     

Costs estimation of an integrated process for the treatment of heavy-metal loaded aqueous effluents

This work aims at providing a guide for the calculation of investment and operation costs of a process to treat diluted streams of heavy metal ions. This process is composed of two stages: (1) a metal concentration stage by polymer supported ultrafiltration; (2) a polymer regeneration and metal recovery by electrodeposition. First of all, the most relevant parameters to be used in the process design will be correlated with the key working variables. Next, these parameters will be related with the cost of the main investment of the plant, providing Williams equations based on both literature and suppliers’ budgets. Finally, a detailed costs calculation for the most representative values of the working variables will be presented as example.     

Facile synthesis of ZnS/WO3 coupled photocatalyst and its application on sulfamethoxazole degradation

In this study, the coupled photocatalysts ZnS/WO₃ were synthesized by a simple co-precipitation method, varying the content of ZnS (1, 5, and 10 wt%). The obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy coupled to energy dispersive spectroscopy (SEM-EDS), N₂ physisorption, UV–Vis with diffuse reflectance spectroscopy (DRS), atomic absorption (AAS), infrared (IR), and photoluminescence (PL) spectroscopies. Furthermore, the synthesized photocatalysts were evaluated on the photocatalytic degradation of sulfamethoxazole (SMX) under simulated sunlight. The activity of the different coupled photocatalysts ZnS/WO₃ was significantly improved compared to the individual semiconductors (ZnS and WO₃). This enhancement was attributed to the reduced recombination rate determined through PL analysis. The ZnS_5%/WO₃ photocatalyst exhibited the highest performance in comparison with the other coupled materials, achieving complete SMX degradation in 60 min. In combination, the enhanced specific surface area, high particle dispersion, and reduced recombination rate define the ZnS_5%/WO₃ photocatalyst as a suitable candidate for photocatalytic environmental applications.