Removal of Emerging Environmental Contaminant Using Sio2-Tio2 Nanocomposite
Published on Feb 27, 2019
The pollution of the environment resulting from the increasing use of human and veterinary pharmaceuticals poses a threat to wildlife and also humans via drinking polluted water. However, monitoring and controlling the presence of pharmaceuticals in the environment is difficult and currently inadequate.
The ability of fish to accumulate high levels of certain pharmaceuticals is alarming. For example, in a study in Sweden, 23 pharmaceuticals have been detected in 7 wild fish (perch) samples . Also, in Sweden, ciprofloxacin (an antibiotic) has been detected in fish at an average concentration of 6 μg/kg. Antidepressant (citalopram) and painkiller (propoxyphene) have similarly been reported in the liver of perch in the Baltic Sea.
Recent investigations for presence of pharmaceuticals, from water treatment plant shows 31,000 μg/L concentration of Ciprofloxacin (antibiotic) in Patencheru Enviro Tech Limited (PETL) near Hyderabad.
Nanotechnology for water and waste water treatment is increasing day by day. The exclusive properties of nanomaterials show a great opportunity for water and wastewater treatment. Silica nanoparticles are of promising applications in many current and emerging areas of technology because of their natural advantages. Silica generally behaves as an insulator. It shows very high refractive index and optical absorbance at high temperature. It has high melting point varying depending on type of the particular structure. Titanium dioxide (TiO2) belongs to the family of transition metal oxides. There are four commonly known polymorphs of TiO2 found in nature anatase (tetragonal), brookite (orthorhombic), rutile (tetragonal) and TiO2 (monoclinic).Titanium dioxide particles in nano form catalyse the oxidation of absorbed molecules in the presence of incident light of adequate photon energy.
The present investigation focuses on removal of an emerging contaminant (Levofloxacin a pharmaceutical compound) from an aqueous environment.
Keywords : TiO2-SiO2 Nanocomposite, Adsorption, Levofloxacin.
To prepare the Silicon dioxide-Titanium dioxide (SiO2-TiO2) nanocomposite.
To study the effect of pH on LFC removal.
To study the effect of contact time on adsorption of levofloxacin.
To study the effect of nanocomposite dosage on adsorption of levofloxacin.
Ultraviolet -visible spectroscopy
Preparation of SiO2-TiO2 nanocomposite
The SiO2-TiO2 nano composite has been obtained using the sol-gel method. In the synthesis of SiO2 particles, tetraethoxysilane (TEOS) (1mole) and tetra-isopropoxide (1 mole) prepared by dissolving in solvent ethanol (60 ml) mixture was stirred for 30 mins, and then added catalyst HCl (1 mole) drop wise into the above mixture and stirred magnetically 60 mins to become a white transparent homogeneous solution. Now the prepared sample is kept for aging about 48 hours for gel preparation at room temperature. The suspensions obtained were dried in an oven for 4 hours at 400°C; crystalline SiO2-TiO2 particles were obtained, then grinded to form SiO2-TiO white powder.
Maximum LFC removal efficiency of 56.2% was observed for contact time of 1440 minutes (i.e., 24 hours) and dosage 500 mg/L.
For pH 6, the LFC removal efficiency of 24% was observed for contact time (after stirring for 30 mins with nanocomposite) of 30 minutes with initial concentration of 5x 10-6 moles/L.
LFC removal efficiency of 61.4% was observed for pH 6 for the SiO2-TiO2 nanocomposite dosage of 500 mg/l and initial LFC concentration of 2 x 10-5 moles/l for contact time (after stirring with nanocomposite) of 30 mins.
The maximum LFC removal observed was 73.2% for 1250mg/l SiO2-TiO2 nano composite dosage with initial LFC concentration 2 x 10-5 and for contact time (after stirring with nanocomposite) of 30 mins. Minimum removal efficiency of 20% was observed for nanocomposite dosage of 125 mg/l.
Initial LFC concentration has direct influence on adsorption of LFC onto SiO2-TiO2 nanocomposite. It was observed that as the initial LFC concentration increases, the LFC removal efficiency decreases. Maximum LFC removal efficiency of 73.2% was observed for minimum initial LFC concentration 1 x 10-6 moles/l.
Contact time is directly proportional to LFC removal efficiency. Maximum LFC removal efficiency of 58.7% was observed for contact time of 60 min.
The experimental results lead to the following conclusions
It can be concluded that LFC removal from aqueous solution can be enhanced by combination of SiO2-TiO2 nanocomposite (with stirring period of 30 mins) and UV light (24 watts with degradation time of 30 mins).
It was observed that maximum LFC removal was attained at pH 6 for 500 mg/l of SiO2-TiO2 nanocomposite dosage, initial LFC concentration of 2x 10-5 moles/l with the total contact time (adsorption time+ degradation time) of 60 mins. This can be attributed to the fact that pka (acid dissociation constant) of LFC is 6.2.
It can be concluded that as the SiO2-TiO2 nanocomposite increases, the surface area available to adsorb LFC also increases. This results in increased LFC removal efficiency.
As the initial LFC concentration increases, the LFC removal efficiency of SiO2-TiO2 nanocomposite decreases. This is due to the fact that as LFC concentration increases, the anion concentration also increases, but the surface area available to adsorb LFC decreases.
SiO2-TiO2 photocatalyst (in presence of UV light) can be used as an advanced treatment technology to remove the pharmaceutical drug from water, so that the disasters like Iska -Vagu lake near Hyderabad can be prevented.
Further investigation needs to be done for other pharmaceutical compounds by using SiO2-TiO2 nano composite.
1. Senthil Kumar K (2012) Pharmaceutical Substances in India are a Point of Great Concern? Hydrol Current Res 3, 103., pp(1-2)
2. Fick J, Lindberg RH, Kay L, Brorstrom-Lunden E (2011). Results from the Swedish National Screening Programme 2010, Subreport 3. pp (22)
3. Lyons, G (2014), Pharmaceuticals in the environment: A growing threat to our tap water and wildlife, A CHEM Trust report.
Project Done By Ms. Anusha Kerutagi, Ms. Anushri Hiramani, Ms. Komal Belgundkar, Mr. Basavaraj Chillalshetti