Adsorption of 2,4,6-trichlorophenol by multi-walled carbon nanotubes as affected by Cu(II)

Adsorption equilibrium of 2,4,6-trichlorophenol (TCP) on multi-walled carbon nanotubes (MWCNTs) was investigated to explore the possibility of using MWCNTs for concentration, detection and removal of TCP from contaminated water. The adsorption of TCP on MWCNTs at pH 4 was nonlinear, reversible and best fit by a Polanyi-Manes model. Oxidation treatment increased surface area and introduced hydrophilic carboxylic groups to the defect sites of MWCNTs, hence increased the sorption of TCP and Cu(II) individually. Cu(II) suppressed the sorption of TCP on oxidized MWCNTs15A, but had little effect on as-grown MWCNTs15. TCP had no influence on Cu(II) sorption to either. The mechanisms of Cu(II) suppression effect on TCP adsorption are ascribed to the formation of surface complexes of Cu(II), which was verified by X-ray absorption spectroscopy. Cu(II) exerts a cross-linking effect of functional groups on adjacent tubes, creating a more tightly knit bundle and suppressing the condensation of TCP in the pore spaces between the tubes. The large hydration sphere around surface complexes of Cu(II) may also intrude or shield hydrophilic sites, leading to the “crowding out” of TCP around the Cu(II)-complexed sites.     

The effects of heat treatment on some technological properties in Uludağ fir (Abies bornmuellerinana Mattf.) wood

Heat treatment is often applied to improve the dimensional stability of woods. In this study, the effect of heat treatment on some mechanical properties of Uluda? fir wood (Abies bornmuellerinana Mattf.) having industrially high usage potential and large plantations in Turkey was evaluated. Samples collected from Bolu Forest Enterprises, Turkey were subjected to heat treatment for varying temperatures and durations. Then, the treated and control samples were tested for some mechanical properties; compression strength, bending strength, modulus of elasticity in bending, janka-hardness, impact bending strength and tension strength perpendicular to grain. The results indicated that treated samples had lower mechanical properties compared to the control samples. In addition, increase in temperature and durations decreased the mechanical properties.     

Separation of hydrocarbons and lipid from water using treated bark

This paper explores the possibility of using treated bark to remove oily compounds from water. Bark was first biologically or chemically treated and saturated with transition metal ions (TMI) to avoid the release of soluble organic compounds from the bark in the treated effluents. Several experimental parameters affecting the oil removal efficiency (RE) were studied (initial oil concentration, temperature, time, etc.). Saturated bark was characterized using Fourier transform infrared (FTIR) spectroscopy and bark wetting index was determined. Results of the retention of lipids suggested that their removal could exceed 95% of initial oil concentration. The uptake of lipid by treated bark varied from 0.2 to 2.0 g of organic oil/g of dry sorbent. No significant chemical modifications of saturated bark were observed in infrared spectroscopy after the sorption of oleic acid on bark treated with transition metal ions. The structure of adsorbed tridimensional layer of oleic acid molecules seemed to take place through the double bond. The hydrocarbon RE exceeded 95% using oil-water mixture with a hydrocarbon/bark ratio of one. The sorption reaction of hydrocarbons and lipids was quasi-instantaneous and seemed to be influenced by the temperature. This indicated that the retention mechanism was related to the capillary action. Results of FTIR spectroscopy suggested that no chemical bonds between barks and oily compounds were established.     

Photocatalytic degradation of 2,4-dinitrophenol (DNP) by multi-walled carbon nanotubes (MWCNTs)/TiO2 composite in aqueous solution under solar irradiation

Nanosized multi-walled carbon nanotubes (MWCNTs)/TiO₂ composite and neat TiO₂ photocatalysts were synthesized by sol-gel technique using tetrabutyl titanate as a precursor. The as prepared photocatalysts were characterized using XRD, SEM, FTIR and UV-vis spectra. The samples were evaluated for their photocatalytic activity towards the degradation of 2,4-dinitrophenol (DNP) under solar irradiation. The results indicated that the addition of an appropriate amount of MWCNTs could remarkably improve the photocatalytic activity of TiO₂. An optimal MWCNTs:TiO₂ ratio of 0.05% (w/w) was found to achieve the maximum rate of DNP degradation. The effects of pH, irradiation time, catalyst concentration, DNP concentration, etc. on the photocatalytic activity were studied and the results obtained were fitted to the Langmuir-Hinshelwood model to study the degradation kinetics. The optimal conditions were an initial DNP concentration of 38.8 mg/L at pH 6.0 with catalyst concentration of 8 g/L under solar irradiation for 150 min with good recyclisation of catalyst. The degree of photocatalytic degradation of DNP increased with an increase in temperature. The MWCNTs/TiO₂ composite was found to be very effective in the decolorization and COD reduction of real wastewater from DNP manufacturing. Thus, this study showed the feasible and potential use of MWCNTs/TiO₂ composite in degradation of various toxic organic contaminants and industrial effluents.     

Chromium removal by combining the magnetic properties of iron oxide with adsorption properties of carbon nanotubes

The adsorption features of multiwall carbon nanotubes (MWCNTs) with the magnetic properties of iron oxides have been combined in a composite to produce a magnetic adsorbent. Composites of MWCNT/nano-iron oxide were prepared, and were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and Fourier transform infrared spectroscopy (FTIR). XRD suggests that the magnetic phase formed is maghemite and/or magnetite. FESEM image shows nano-iron oxides attached to a network of MWCNTs. The adsorption capability of the composites was tested in batch and fixed bed modes. The composites have demonstrated a superior adsorption capability to that of activated carbon. The results also show that the adsorptions of Cr(III) on the composites is strongly dependent on contact time, agitation speed and pH, in the batch mode; and on flow rate and the bed thickness in the fixed bed mode. Along with the high surface area of the MWCNTs, the advantage of the magnetic composite is that it can be used as adsorbent for contaminants in water and can be subsequently controlled and removed from the medium by a simple magnetic process.     

Modification of low pressure membranes with carbon nanotube layers for fouling control

Carbon nanotubes (CNTs) with different physiochemical properties were layered onto low pressure membranes and tested for antifouling properties using a natural surface water with high fouling potential. Membranes modified with the largest diameter pristine multi-walled CNTs (MWCNTs) were most effective in controlling membrane fouling, tripling the time it took for the membrane to become noticeably fouled at a CNT loading of 22 g/m². The differences in the structure of CNT layers were an important contributing factor for antifouling properties; scanning electron microscopy imaging showed that large diameter MWCNTs formed homogeneous porous layers across the membrane surface, while less effective, small diameter MWCNTs formed heterogeneous layers. Water quality analysis showed that CNT-membranes constructed with larger diameter CNTs were more effective at removing larger organic macromolecules responsible for fouling from feedwater compared to membranes made with smaller diameter CNTs. This reduced the concentration of foulants reaching the PVDF membrane and thus helped reduce membrane fouling. Beneficial for application, increased loadings of CNTs onto the membrane surface increased resistance to fouling while only slightly reducing the clean water permeability of the modified membranes. Overall, CNT layered membranes were shown to highly resist membrane fouling with potential applications in sustainable water treatment.     

Mechanical and chemical behavior of spruce wood modified by heat

In this study the effects of heat treatment on compression strength (CS) of spruce wood (Picea orientalis) were examined and changes in the chemical structure of the treated wood were determined by analyzing contents of cellulose, hemicellulose and lignin.

Heat treatment was applied on the test samples in an oven at four different temperatures (130, 150, 180 and 200 °C) and three different durations (2, 6 and 10 h) under atmospheric pressure.

The results indicate that the effects of heat treatment on CS values generally exhibited a decrease with increased duration and temperature. It was seen that hemicelluloses were the wood-cell components most degraded by the heat treatment.     

Experimental investigation of the effect of carbon nanotubes and carbon fibres on the behaviour of plain cement composite beams

In this article, the behaviour of reinforced cement composite beams with multi-walled carbon nanotubes (MWCNTs) and carbon fibres (CFs) is investigated. The percentage of CFs was fixed at 0.25 wt% of cement, while the percentage of MWCNTs was varied from 0.25, 0.5, 0.75, 1 wt% of cement. Dispersion of both MWCNTs and CFs was carried out using ultrasonic energy. Composite beams were tested under flexure in order to evaluate their mechanical properties such as flexural strength, toughness and ductility. These results were then compared with the results of plain cement control beams. The present work also investigates the optimum percentage of fibres that gives the best results both in terms of enhanced properties and economy.     

Removal of fulvic acid from water electrochemically using active carbon fiber electrode

Humic acids (HA) are a group of widely existing natural organic compounds and potential contaminants to underground water reservoirs. Fulvic acid (FA) is a typical humic acid of relatively low molecular weight. Electrochemical removal of FA from water by active carbon fiber (ACF) electrodes was studied by using light scattering photometer (LSP), fluorescence spectroscopy and total organic carbon analyzer (TOC). The experiments showed that FA molecules aggregated and that the average particle diameter in FA solution increased from below 10 nm to hundreds of nanometers during the treatment process. When iron was added to the anode, the FA could be coagulated efficiently at the early stage of the treatment. The proposed mechanism of the removal process is: adsorption of FA on ACF surface→aggregation of FA→desorption of FA aggregates from ACF→coagulation of FA aggregates by nFe(OH)₂√mFe(OH)₃ dissolved from anode. Experiments were also repeated using graphite and stainless-steel electrodes, and the results were compared with that of ACF electrodes. FA aggregation was not observed in these experiments and most FA was not removed from the solution. At the end of this paper, FA samples from Huai River sediment were successfully treated using the ACF electrode.     

Transport behavior of functionalized multi-wall carbon nanotubes in water-saturated quartz sand as a function of tube length

A series of one-dimensional column experiments was conducted to examine the effects of tube length on the transport and deposition of 4-ethoxybenzoic acid functionalized multi-wall carbon nanotubes (MWCNTs) in water-saturated porous media. Aqueous MWCNTs suspensions were prepared to yield three distributions of tube lengths; 0.02-1.3 μm (short), 0.2-7.5 μm (medium), and 0.2-21.4 μm (long). Results of the column studies showed that MWCNT retention increased with increasing tube length. Nevertheless, more than 76% of the MWCNT mass delivered to the columns was detected in effluent samples under all experimental conditions, indicating that the functionalized MWCNTs were readily transported through 40-50 mesh Ottawa sand. Examination of MWCNT length distributions in the effluent samples revealed that nanotubes with lengths greater than 8 μm were preferentially deposited. In addition, measured retention profiles exhibited the greatest MWCNT deposition near the column inlet, which was most pronounced for the long MWCNTs, and decreased sharply with travel distance. Scanning electron microscope (SEM) images showed that MWCNTs were deposited on sand surfaces over the entire column length, while larger MWCNT bundles were retained at grain intersections and near the column inlet. A mathematical model based on clean bed filtration theory (CBFT) was unable to accurately simulate the measured retention profile data, even after varying the weighting function and incorporating a nonuniform attachment rate coefficient expression. Modification of the mathematical model to account for physical straining greatly improved predictions of MWCNT retention, yielding straining rate coefficients that were four orders-of-magnitude greater than corresponding attachment rate coefficients. Taken in concert, these experimental and modeling results demonstrate the potential importance of, and need to consider, particle straining and tube length distribution when describing MWCNT transport in water-saturated porous media.     

Dissolved organic matter in leachate from different treatment processes

The main objectives of this study were to investigate the characteristics of dissolved organic matter (DOM) extracted from the leachate of different treatment process using the chemical and spectroscopic analysing methods. The humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) were isolated and purified by the XAD-8 resin combined with the cation exchange resin method. The analytical results of fluorescence excitation-emission matrix spectroscopy (EEMs) revealed that the fluorescence peaks were protein-like fluorescence for equalization basin and discharge of reverse osmosis (RO), while the fluorescence peaks for second sedimentation tank were humic-like and fulvic-like fluorescence. Moreover, the results also showed that protein-like organic matter are readily removed by biological process and HA and FA can be removed by RO process. Elemental analysis indicated that the nitrogen content in these isolated fractions followed: HA>HyI>FA. The information on the characteristics of DOM indicated important role in optimization of leachate treatment processes.     

Carbon nanotube blended polyethersulfone membranes for fouling control in water treatment

Multi-walled carbon nanotube/polyethersulfone (C/P) blend membranes were synthesized via the phase inversion method. The resultant membranes were then characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and contact angle. The C/P blend membranes appeared to be more hydrophilic, with a higher pure water flux than the polyethersulfone (PES) membranes. It was also found that the amount of multi-walled carbon nanotubes (MWCNTs) in the blend membranes was an important factor affecting the morphology and permeation properties of the membranes. After 24 h of surface water filtration with 7 mgC/L TOC content, the C/P blend membranes displayed a higher flux and slower fouling rate than the PES membranes. Subsequent analyses of the desorbed foulants showed that the amount of foulant on bare PES membranes was 63% higher than the C/P blend membrane for 2% MWCNTs content. Thus, the carbon nanotube content of the C/P membranes was shown to alleviate the membrane fouling caused by natural water.     

Synthesis and characterisation of multi-walled carbon nanotubes (MWCNTs)

ABSTRACT

Carbon nanotubes are one of the major research areas in the field of nanotechnology, due to its mechanical and electro-conductive properties in the field of engineering and medical sciences. This paper focuses on preparation of multi-walled carbon nanotubes (MWCNTs) for the mass production using thermal catalytic chemical vapour deposition method. The synthesis of MWCNTs was made by breakdown of acetylene (C₂H₂) gas and Fe/MgO acting as catalyst. The surface morphology and structure of MWCNTs were characterised by scanning electron microscopy (SEM). Also phase identification and crystalline size of the nanopowder were determined by XRD. The particle size of MWCNTs was verified by SEM analysis and it was in the range of 20–30?nm and elemental analysis was carried out through energy dispersive analysis X-ray. Furthermore, thermal decomposition of the material property was studied by thermogravimetric analysis.     

IMPROVING THE PERFORMANCE OF GRANULAR ACTIVATED CARBON (GAC) VIA PRE-REGENERATION ACID TREATMENT

A lab-scale acid treatment system was developed to Investigate the effects of hydrochloric acid on the removal of calcium from field spent GAC (FSGAC). The effects of acid treatment on the subsequent regeneration process and regenerated GAC properties were also investigated using a lab-scale furnace. A linear relationship between calcium remaining on the GAC following acid treatment and GAC mass losses during regeneration was exhibited. FSGAC treated with 0.1 N hydrochloric acid resulted in 7.5% lower mass losses than non-acid treated GAC. An increase in total surface area of 7.2% and micropore volume of 3.1% was also noted following acid treatment and regeneration. This was due to a reduction in calcium-catalysed gasification of the GAC structure, which may have occurred in samples, which had not received acid treatment. Improvements in porosity, adsorption capacity and surface chemistry indicate that acid treatment is an effective process, which may be used to provide superior regenerated GAC product.     

Vibration analysis of multi-walled carbon nanotubes embedded in elastic medium

We propose a method to estimate the natural frequencies of the multi-walled carbon nanotubes (MWCNTs) embedded in an elastic medium. Each of the nested tubes is treated as an individual bar interacting with the adjacent nanotubes through the inter-tube Van der Waals forces. The effect of the elastic medium is introduced through an elastic model. The mathematical model is finally reduced to an eigen value problem and the eigen value problem is solved to arrive at the inter-tube resonances of the MWCNTs. Variation of the natural frequencies with different parameters are studied. The estimated results from the present method are compared with the literature and results are observed to be in close agreement.     

Use of three-dimensional excitation and emission matrix fluorescence spectroscopy for predicting the disinfection by-product formation potential of reclaimed water

This study was undertaken to demonstrate the feasibility of using three-dimensional excitation-emission matrix (3DEEM) fluorescence spectroscopy for the determination of chlorination disinfection by-product (DBP) precursors and the disinfection by-product formation potential (DBPFP) of reclaimed water samples. Two major DBP precursors were examined in this study, including humic acid (HA) and fulvic acid (FA). The 3DEEM fluorescence results obtained from various reclaimed water samples indicated that the reclaimed water samples were rich in fulvic acid-like substances that were associated with two main peaks (Ex/Em = 235-245/420-440 nm, and Ex/Em = 330-340/410-430 nm) in the fluorescence spectrum. The results also illustrated that the wavelength location of peak fluorescence intensity of a reclaimed water sample was independent of the influent water quality and the wastewater treatment process used in the reclamation plant. As a result, the peak fluorescence intensity and the wavelength location of the peak were used to identify the species of DBP precursors and their concentrations in the reclaimed water sample. Four regression models were then developed to relate the peak fluorescence intensity of the water sample to its DBPFP, including the formation potential of trihalomethane (THMFP) and the formation potential of haloacetic acid (HAAFP). The regression models were verified using the measured DBPFP results of a series of reclaimed water samples. It was found that the regression modeling results matched the measured DBPFP values well, with prediction errors below 10%. Therefore, the use of 3DEEM fluorescence spectroscopy together with the developed regression models in this study can provide a reliable and rapid tool for monitoring the quality of reclaimed water. Using this method, water quality could be monitored online, without utilizing the lengthy conventional DBPFP measurement.     

Advanced cement based nanocomposites reinforced with MWCNTs and CNFs

Cementitious materials reinforced with well dispersed multiwall carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) at the nanoscale were fabricated and tested. The MWCNTs and CNFs were dispersed by the application of ultrasonic energy and the use of a superplasticizer. Mechanical and fracture properties including flexural strength, Young’s modulus, flexural and fracture toughness were measured and compared with similarly processed reference cement based mixes without the nano-reinforcement. The MWCNTs and CNFs reinforced mortars exhibited superior properties demonstrated by a significant improvement in flexural strength (106%), Young’s modulus (95%), flexural toughness (105%), effective crack length (30%) and fracture toughness (120%).     

Adsorption of chloridazon from aqueous solution on heat and acid treated sepiolites

The adsorption of chloridazon on heat treated sepiolite samples at 110 degrees C (S-110), 200 degrees C (S-200), 400 degrees C (S-400), 600 degrees C (S-600) and acid treated samples with H2SO4 solutions of two different concentrations (0.25 and 1.0M) (S-0.25 and S-1.0, respectively) from pure water at 25 degrees C has been studied by using batch experiments. In addition, column experiments were carried out with the natural (S-110) and 600 degrees C (S-600) heat treated samples, using a 10.30 mg l-1 aqueous solution of chloridazon. The adsorption experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (Kf) of the samples; Kf values range from 2.89 mg kg-1 for the S-1.0 sample up to 164 mg kg-1 for the S-600 sample; so, the heat treatment given to the sepiolite greatly increases its adsorption capacity for the herbicide chloridazon whereas the acid treatment produces a clear decrease in the amount of chloridazon adsorbed. The removal efficiency (R) has also been calculated; R values ranging from 5.08% for S-1.0 up to 60.9% for S-600. The batch experiments showed that the strongest heat treatment is more effective than the natural and acid treated sepiolite in relation to adsorption of chloridazon. The column experiments also showed that 600 degrees C heat treated sepiolite might be reasonably used in removing chloridazon from water. Thus, as this type of clay is relatively plentiful, these activated samples might be reasonably used in order to remove chloridazon from water.     

Evaluation of effect of leaching medium on the release of copper,chromium, and arsenic from treated wood

There is increasing public concern about environmental contamination from preservative treated wood due to release of toxic preservative components to the environment. Leaching of wood preservatives from treated wood in service can be affected by a number of factors such as wood and preservative treatment characteristics and properties of water and soil substrate in which treated wood is placed i.e. salinity, pH, and temperature. Laboratory leaching tests usually require distilled or deionized water for leaching procedure however treated wood is generally exposed to different types of water and soil conditions. This study evaluates the release of copper, chromium and arsenic elements from chromated copper arsenate (CCA)-treated wood exposed to either distilled water, tap water, sea water or humic acid. Leaching tests were conducted in laboratory conditions using wood blocks treated with CCA wood preservative at either low or high retention levels. Results showed that tap water resulted in less preservative release when compared to the other leaching media used in the study. Humic acid was the most effective medium causing more element leaching. The percentage of components leached was always higher in wood blocks treated at the high retention in comparison with the low retention level. Our results from the leaching tests can be important in developing more realistic standard leaching methods to evaluate preservative components to be released from treated wood.     

Effects of priming with multi-walled carbon nanotubes on seed physiological characteristics of Hopbush (Dodonaeaviscosa L.) under drought stress

This paper reports the effects of different dosages of multi-walled carbon nanotubes (MWCNTs) on seed germination of hopbush, a medicinal multipurpose plant. After nano-priming and drying under room temperature, the seeds were placed in a germinator under 20 °C constant temperature and 65% relative humidity with a photoperiodic regime of 16 h light/8 h dark at 1000 lux fluorescent light. The results show that MWCNTs can dramatically improve seed germination percentage, mean germination time (MGT), root and stem lengths, as well as fresh and dry weights of root and stem. When no drought stress was applied, germination percentage of 10 and 200 mg/l nano carbon treatments was found to be 100%, and MGT in all the studied treatments had a marked decrease as compared to that of the control counterparts. The best results were gained at zero osmotic pressure, in which the effect of CNTs treatment on the mentioned traits was maximal at 30 mg/l. Increasing the level of drought stress revealed that 50 and 100 mg/l dosages of MWCNTs could more favourably affect both the hopbush growth parameters and seed germination. Therefore, nano-priming with carbon tubes can be recommended for enhancing seed germination and plant growth in work on afforestation with hopbush, an evergreen shrub suitable for desert conditions.