Accelerated removal of nitrate from aqueous solution by utilizing polyacrylic anion exchange resin with magnetic separation performance

In order to quickly remove nitrate from aqueous solution, a magnetic strong base quaternary ammonium anion exchange resin (MAER) has been successfully designed and synthesized. The physicochemical properties of the MAER as well as its adsorption ones for nitrate removal were investigated in detail. A series of batch experiments were carried out to evaluate the effects of several factors on removal efficiency of nitrate, such as retention time, resin amount and initial nitrate concentration. Compared to the commercial Purolite A300 and D213, the equilibrium time for the adsorption process using MAER was only around 20 min, which is significantly less than that of two ones mentioned. Furthermore, the kinetic process of nitrate sorption on MAER could be well described by both pseudo-first-order and pseudo-second-order models. In addition, the results of batch experiments can be better fitted by the Langmuir and Freundlich adsorption isotherm models. Most importantly, the effects of competing ions on nitrate removal followed the order as: SO₄²⁻ > Cl⁻ > HCO₃⁻. These results are of significance in guiding the development of novel resins with the rapid nitrate removal rate from aqueous solution, which would improve efficiency and save energy greatly.     

Experimental study of oxytetracycline retention by adsorption onto polyaniline coated peanut shells

The release of drugs and their metabolites into the environment is of a great concern, as far as the water pollution is concerned. One can cite oxytetracycline which is used in large quantities and it is essential to reduce its presence in aquatic environments.     

Preparation and stability behavior of the colloidal epoxy-1,1-iminodi-2-propanol adducts

Epoxy-amine adduct was prepared by reaction between DGEBA and 1,1-iminodi-2-propanol. The kinetic of the reaction was investigated by differential scanning calorimetry (DSC) and a model-free approach. The epoxy-amine adducts were prepared with various molar ratios of amine functionalities. Waterborne dispersions of these resins have been prepared by neutralization of amine functionalities in the epoxy-amine adducts. Fourier Transform Infrared Spectroscopy (FTIR) and DSC were also used to characterize the prepared epoxy-amine adducts. The stability behavior of the neutralized epoxy-amine adducts has been studied at 25 °C in aqueous solution of acetic acid. In each case, the experimental stability ratios (W) versus electrolyte concentration plots were fitted using the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and modified Fuch's model. The resulted values of diffuse potentials and Hamaker constants were obtained for the aqueous dispersions of the epoxy-amine adducts. According to the resulted Hamaker values, the applicability of the DLVO theory to the colloidal particles of epoxy amine adducts was investigated. The cathodic electrodeposition behavior of the prepared dispersions were also investigated. It was found that the samples with lower degree of neutralization result in a more efficient film deposition followed by higher dry film thickness although they show lower stability in the electrodeposition bath.     

Kinetic model and prediction for coal hydrogasification

Coal hydrogasification is a key component of zero emission coal (ZEC) power generation system which discharges little CO₂ and other pollutants at a thermal efficiency close to 70%. In addition, coal hydrogasification itself has many advantages. A hydrogasification kinetic model including ten homogeneous reactions and four heterogeneous reactions is established in this work and is validated against experiment data available in literatures. The validated model is then used to predict the effects of different reaction conditions including the reaction temperature T, the reaction pressure p_t, the H₂/coal mass ratio U and the reaction time t on coal hydrogasification properties. The results indicate that coal hydrogasification is facilitated by the increased p_t and t. When T is not higher than 1273 K, the gasification process is promoted with T increment. Increasing U can promote the coal hydrogasification process on the whole. When U is larger than 0.5, however, the coal conversion ratio (x_coal) will slightly decrease with U increment.     

In situ structure–activity correlation experiments of the ruthenium catalyzed CO oxidation reaction

The complex structure–activity correlation of the CO oxidation on ruthenium has been studied in a batch reactor by using in situ surface X-ray diffraction (SXRD) and on-line mass spectrometry. Two distinct active phases are identified at higher pressures in the mbar range depending on the reaction conditions: a non-oxidic phase and a RuO₂(1 1 0) layer of variable thickness ranging from 1.5 nm to 10 nm. For reaction temperatures lower than 520 K the experimental turnover frequency (TOF) numbers are shown to be almost identical for the two types of active phases. Above 520 K the RuO₂(1 1 0) layer turned out to be much more active than the non-oxidic phase. Kinetic reaction experiments on the RuO₂(1 1 0) phase reveal an activation energy of 78 ± 10 kJ/mol which is in perfect agreement with corresponding reactivity experiments on supported and powder RuO₂ catalyst. Under oxidizing reaction conditions and high concentration of CO₂ in the gas mixture, the RuO₂(1 1 0) model catalyst shows reversible product-poisoning.     

Optimal Growth Conditions for Selective Ge Islands Positioning on Pit-Patterned Si(001)

We investigate ordered nucleation of Ge islands on pit-patterned Si(001) using an original hybrid Kinetic Monte Carlo model. The method allows us to explore long time-scale evolution while using large simulation cells. We analyze the possibility to achieve selective nucleation and island homogeneity as a function of the various parameters (flux, temperature, pit period) able to influence the growth process. The presence of an optimal condition where the atomic diffusivity is sufficient to guarantee nucleation only within pits, but not so large to induce significant Ostwald ripening, is clearly demonstrated.     

Intensification of biodiesel production from vegetable oils using ultrasonic-assisted process: Optimization and kinetic

Intensification of biodiesel production process using low frequency ultrasonic irradiation (20 kHz, 200 W) is elucidated in this study. Effects of five process variables in an ultrasonic-assisted reactor catalyzed by SrO through transesterification of vegetable oils are investigated. RSM was employed and the optimum conditions were at an ultrasonic pulse on of 9 s followed by 2 s of pulse off within a reaction time of 30.7 min. The optimum ultrasonic power was found to be 130 W using an oil amount of 52 g (R² = 0.97). The model was applicable to different types of oil with errors less than 10%. FFA content was responsible for the different yields obtained with different oils. Three steps of the transesterification process were measured to obtain the kinetic study. The results revealed that the reaction followed a second-order kinetic. The activation energies varied between 70.63 kJ/mol and 136.93 kJ/mol showing relatively high coefficient of determinations.     

Experimental methods designed for measuring corrosion in highly resistive and inhomogeneous media

Corrosion measurement in highly resistive and inhomogeneous media can be very challenging due to practical difficulties in setting up and maintaining testing cells and sensors, problems associated with IR potential drops and nonuniform polarisation current distribution, and limitations associated with localised corrosion monitoring and detection. Many technological innovations have been made over the past decade to address these issues with reports scattered throughout the literature. This paper provides an overview of innovative experimental methods designed for corrosion testing and monitoring in highly-resistive and inhomogeneous media, with particular focus on localised corrosion measurement using electrode array and electrochemical noise techniques.     

Understanding the effects of electrode inhomogeneity and electrochemical heterogeneity on pitting corrosion initiation on bare electrode surfaces

The effects of electrode inhomogeneity (EI) and electrochemical heterogeneity (EH) on pitting corrosion initiation have been analysed by revisiting research findings reported in the literature and experimental evidences obtained in our laboratories using the wire beam electrode (WBE) method. Two mechanisms of pitting corrosion initiation have been identified on bare metal surfaces exposed directly to electrolytes. For WBE surface under free corrosion or low anodic polarisation conditions the initiation of pitting corrosion was found to be due to the disappearance of minor anodes, leading to accelerated dissolution of a few remaining major anodes. The nucleation stage of pitting corrosion appeared to be controlled by EI, while the propagation stage appeared to be determined by EH. For WBE surface under large anodic polarisation the initiation of pitting corrosion was found to be due to the formation of active new anodic sites, which is in agreement with the conventional mechanism of pitting nucleation.     

Oxidation kinetics of polyacrylonitrile-based carbon fibers in air and the effect on their tensile properties

Polyacrylonitrile-based carbon fibers are oxidized by air at temperatures from 400 to 700 °C. The mass loss, morphology, graphitic structure and residual properties are investigated. The activation energy is about 111 kJ/mol and is independent of carbonization temperature. With increasing oxidation temperature, the crystallite height decreases gradually, while the d₀₀₂ spacing increases presumably due to combination of oxygen with carbon. The tensile strength decreases significantly, while the tensile modulus remains nearly unchanged. The increase in carbon fiber density after oxidation suggests that glass-like carbon in the fiber is easier to burn off than the more graphitic carbon.