Development of highly efficient and reusable magnetic nitrogen-doped carbon nanotubes for chlorophenol removal.

Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized via a hydrothermal method and further modified with magnetic Co0.5Cu0.5Fe2O4 nanoparticles following a one-pot solvothermal method. The characterization data show that the distribution of the magnetic materials and the adsorption characteristics of the CNTs can be tailored as a function of the N doping amount. The N-CNT adsorption isotherms as a function of N content and chlorophenol uptake show that a N doping level of 6% is optimum. After loading the N-CNTs with the magnetic Co0.5Cu0.5Fe2O4 nanoparticles (M-N-CNTs), the resulting materials were easily dispersed in aqueous media with specific surface area reaching 95.64 m2/g. The M-N-CNTs exhibit high affinities toward the adsorption of different chlorophenols following the order: Pentachlorophenol (PCP) > 2,4,6-trichlorophenol (2,4,6-TCP) > 2,4-dichlorophenol (2,4-DCP) > 2,4-dichlorophenoxyacetic acid (2,4-D) > phenol. Additionally, the M-N-CNTs exhibit good microwave absorption performance and can be regenerated by microwave irradiation with high efficiencies (> 90%) maintained with high stabilities.

An efficient method for removal of pentachlorophenol using adsorption and microwave regeneration with different magnetic carbon nanotubes.

Various magnetic carbon nanotubes (CNTs) Co0.5M0.5Fe2O4-CNTs (M = Cu, Mn, Ni, Zn) were successfully prepared and applied for treatment of pentachlorophenol (PCP) with adsorption and microwave irradiation process. The Co0.5M0.5Fe2O4-CNTs were characterized by transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry, and microwave absorption spectroscopy. The adsorption experiment results showed the adsorption capacity for PCP was in the following order: Co0.5Cu0.5Fe2O4-CNTs > Co0.5Mn0.5Fe2O4-CNTs > Co0.5Ni0.5Fe2O4-CNTs > Co0.5Zn0.5Fe2O4-CNTs. After adsorption, the Co0.5M0.5Fe2O4-CNTs was separated by magnetic field and regenerated by microwave irradiation at 850 W for 180 s. It was confirmed that after six adsorption and microwave regeneration cycles, the regeneration efficiency maintained over 90%. In particular, Co0.5Cu0.5Fe2O4-CNTs exhibited excellent adsorption capacity and reusability. These results can open a new avenue for treatment of chlorinated organic compounds with efficiently and non-secondary pollution.

Adsorption of Tetracycline by Shrimp Shell Waste from Aqueous Solutions: Adsorption Isotherm, Kinetics Modeling, and Mechanism.

The highly efficient removal of tetracycline (TC) from an aqueous solution was accomplished by using the raw shrimp shell waste (SSW) as an environmentally friendly adsorbent. The SSW without any treatment removed TC more efficiently than the SSW after being treated with HCl and NaOH solutions. The SSW was characterized using nitrogen adsorption-desorption isotherms, scanning electron microscopy alongside energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, a thermogravimetric-derivative thermogravimetry analyzer, and a ζ-potential analyzer. The maximum adsorption capacity of 400 mg/L SSW was 229.98 mg/g for 36 h at 55 °C. Both the Langmuir isotherm model and the pseudo-second-order kinetic model well described the experimental data. According to the values of the Gibbs free energy and enthalpy changes, the TC adsorption by SSW proved to be spontaneous and endothermic. The TC adsorption process was controlled by intraparticle diffusion and liquid film diffusion.

Application of weak ultrasonic treatment on sludge electro-osmosis dewatering.

Ultrasonic treatment is a good method of facilitating sewage sludge dewatering characteristics. It can also promote the potential of sludge electro-osmosis dewatering (EDW), which is an accepted method of deep dewatering, but the treatment method and optimizing conditions should be determined by performing experiments. In this study, we consider two treating methods: ultrasonic pre-treatment, which uses ultrasonic treatment as sludge pre-treatment before electro-osmosis dehydration, and ultrasonic coupling, which uses ultrasonic and electric fields simultaneously. Using sludge from the Tianjin Jizhuangzi sewage treatment plant, we analyze the influence of ultrasonic intensity and treatment time on sludge dewatering by performing two different methods. The results show that they effectively facilitated sludge EDW. Under the same conditions, i.e. 2 cm cake initial thickness, voltage of 60 V for 5 min, and 0.1 MPa mechanical pressure for 5.5 min, the optimum processing conditions for ultrasonic pre-treatment were found to be 0.510 W/cm2 and 3.5 min, the dehydration rate reached 34.71%, and the optimum conditions for ultrasonic coupling were 0.255 W/cm2 and 3.5 min, while the dehydration rate reached 40.78%. The dehydration rates for both approaches were clearly better than 17.40%, which was obtained under pure electro-osmosis dehydration. To compare the effects of ultrasonic pre-treatment and ultrasonic coupling on the electro-osmosis dehydration process, in this paper, we present the curves of dehydration rate, electric current, electro-osmosis flow, and scanning electron microscopy for dewatered sludge. Compared with the ultrasonic pre-treatment method, the effect of ultrasonic coupling on electro-osmosis dehydration was more obvious.

Assessment of long-range transport potential of polychlorinated Naphthalenes based on three-dimensional QSAR models.

Experimentally determined octanol-air partition coefficients (K OA) for 43 polychlorinated naphthalene (PCN) congeners and experimentally determined subcooled liquid vapor pressures (P L) for 17 PCN congeners were used with comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) to generate three-dimensional quantitative structure-activity relationship (3D-QSAR) models. The data were used to predict K OA values for the other 32 congeners and P L values for the other 58 congeners. The CoMFA and CoMSIA model contour maps showed that the electrostatic fields of the PCN molecules are the most important factors affecting the K OA and P L values. The long-range transport potentials of several PCN homologs were assessed using the following grading system: high mobility (MoCNs), relatively high mobility (DiCNs to TeCNs), relatively low mobility (PeCNs to HeCNs) and low mobility (HeCNs and OCN). The PCN-2 molecule was modified using the contour maps of the two models, and the results showed that introducing an electronegative R1 substituent increased the K OA value but introducing an electropositive R6 substituent decreased the P L value. PCN-2 was in the high mobility class, but introducing these substituents moved the long-range transport potentials of the modified molecules to the relatively high mobility class.

Electrochemically enhanced adsorption of phenol on activated carbon fibers in basic aqueous solution.

Electrosorption isotherms and thermodynamics of phenol on activated carbon fibers (ACFs) in basic solution, as well as the factors (bias potential, initial concentration, and electrolyte) affecting adsorption/electrosorption kinetics, were investigated. The kinetics, which followed the Lagergren adsorption rate law, exhibited a variety of responses depending on bias potential, initial concentration, and electrolyte. The electrosorption isotherms were in agreement with the classical models of Langmuir and Freundlich, but the former gave more satisfactory correlation coefficients. With electrosorption at a bias potential of 700 mV from the basic solution, a nearly 10-fold enhancement of maximum adsorption capacity was achievable. The electrosorption free energy (DeltaG(ads)), enthalpy (DeltaH(ads)), and entropy (DeltaS(ads)) of phenol on the ACFs were calculated from adsorption isotherms at different temperatures. The results indicated that electrosorption of phenol in basic solution was spontaneous and exothermic. Furthermore, it was assessed that electrosorption occurred by dipole-dipole interaction with DeltaH(ads) of -20.14 kJ mol(-1) besides suppositional electrostatic interaction.