Patent Application
20150136703
1. Field of the Invention
The present invention relates to water purification compositions and processes, and particularly to titanium-impregnated carbon nanotubes for selenium removal from water.
2. Description of the Related Art
Selenium can be considered a nutrient for humans and animals when present in trace quantities. However, selenium can also be toxic to humans and animals in larger concentrations. Relatively toxic amounts of selenium can contaminate water in a number of ways, such as through the weathering of natural rock, or through manufacturing operations. Types of manufacturing operations that can lead to selenium contamination include the manufacturing of pigmented glass, lubricants, or rubber, among others. Different techniques have been investigated to eliminate or reduce selenium levels in water, including reverse osmosis and adding adsorbents, such as activated charcoal, to the water.
Nanotubes, particularly carbon nanotubes, have attracted considerable research interest because of their mechanical-electrical properties, relatively higher chemical stability, and relatively larger specific area. Further, multi-walled carbon nanotubes have been previously used in removing metal ions, such as lead, copper, cadmium, silver, and nickel, from water.
Thus, titanium-impregnated carbon nanotubes for selenium removal solving the aforementioned problems is desired.
The titanium-impregnated carbon nanotubes for selenium removal provide a composition for removing or reducing the levels of selenium in water. The titanium-impregnated carbon nanotubes comprise a range of about 5 wt % titanium to 20 wt % titanium. A process for removing selenium from water includes the steps of placing the titanium-impregnated carbon nanotubes into contact with the water and adjusting the pH value of the water.
These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.
Similar reference characters denote corresponding features consistently throughout the attached drawings.
The titanium-impregnated carbon nanotubes for selenium removal are fabricated by impregnating multi-walled carbon nanotubes (MWCNTs) with titanium (Ti). The titanium-impregnated carbon nanotubes (Ti/CNTs) possess a relatively improved capacity to remove selenium from water. The following examples illustrate synthesis and testing of the titanium-impregnated carbon nanotubes for selenium removal.
Samples of the Ti/CNTs were synthesized as follows. About 0.25 grams of titanium isopropoxide was dissolved in about 200 milliliters (ml) of ethanol solution and mixed with about 4.75 g of MWCNTs to prepare carbon nanotubes impregnated with titanium nanoparticles having 5 weight (wt) % titanium (Ti-5/CNTs). The MWCNTs were prepared using a Floating Catalyst Chemical Vapor Deposition (FC-CVD) reactor.
The solution was mixed using an ultrasonic mixer for a time period of about 30 minutes. After mixing, the solution was placed inside a beaker, which was then placed inside a furnace at a temperature in a range of about 60° C. to 80 ° C. over the course of the night for evaporation of ethanol present in the solution, thus forming a product. After the overnight time period had elapsed, the product was placed inside an oven at about 350° C. for a period of about 3 hours for calcination. To prepare the samples having 10 wt % titanium (Ti-10/CNTs) and 20 wt % titanium (Ti-20/CNTs), the same procedures were followed but with different quantities, i.e., 0.5 g of titanium isopropoxide being mixed with 4.5 g of MWCNTs to yield Ti-10/CNTs samples (10 wt %) and 1 g of titanium isopropoxide being mixed with 4 g of MWCNTs to yield Ti-20/CNTs samples (20 wt %).
A stock solution of aqueous selenium was prepared by dissolving a proper amount of selenium dioxide (SeO2) in deionized water, depending on the required concentration. The pH of the stock solution was adjusted by using either 0.1 M nitric acid or 0.1 M sodium hydroxide (NaOH). Lastly, buffer solutions were added to the stock solution to maintain the pH constant during the experiments. The materials used in preparing the Ti/CNTs samples and the stock solution of aqueous selenium were of analytical reagent grade and used as received without pretreatment. Titanium isopropoxide, SeO2, nitric acid, sodium hydroxide, and ethanol were purchased from Sigma-Aldrich.
Batch mode adsorption experiments were conducted at room temperature to investigate the effect of pH of the Se solution, contact time, carbon nanotube dosages, and initial concentration of Se ions on the adsorption of Se ions. The experiments were carried out in volumetric flasks, and the initial and final concentrations of Se ions were analyzed by using Inductively Coupled Plasma (ICP).
The study of sorption kinetics can be used to express the adsorbate uptake rate as a function of the residence time of adsorbate at the solid/liquid interface. The pseudo-second-order rate equation can be expressed as:
where qe is a sorption capacity (mg/g) at equilibrium, qt is a sorption capacity (mg/g) at time t, t is time (min), and K2 is the rate constant of the pseudo-second-order sorption, given as g·mg−1·min−1.
Adsorption isotherm models are used to describe the distribution of the adsorbate species between liquid and adsorbent. The Langmuir and Freundlich isotherms were used to study the adsorption performance and to calculate the adsorption capacity for the adsorbent. The Langmuir adsorption isotherm is expressed as:
where Qe is the amount adsorbed (mg/g), Ce is the equilibrium adsorbate concentration (mg/l), KL is the Langmuir constant, and qm is the maximum adsorption capacity (mg of adsorbate adsorbed per g of adsorbent). Equation (2) can be linearized as follows:
The Freundlich isotherm is expressed as:
Q
e
=K
f
C
3
1/n (4)
Equation (3) can be linearized as follows:
where: Kf and n are the empirical constants that depend on several environmental factors.
The pH of the Se solution is a relatively important factor that can control the adsorption of Se ions on the adsorbent surface. When pH of the Se solution is lower than the Point of Zero Charge (pHPZC), the positive charge on the surface provides electrostatic interactions that are favorable for adsorbing anionic species.
Referring to
Referring to
As shown in plot 200 of
Referring to
Referring to
Referring to
Referring to
Referring to
Table 1 shows the parameters of the Langmuir and the Freundlich adsorption isotherm models of Se. The maximum adsorption capacity of Ti-10/CNT is 55.56 (mg/g). Therefore, it was verified that CNTs have a relatively great potential to be excellent adsorbents for the removal of selenium ions in water treatment.
It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.
