removal of Ag(I), and Pb(II) from aqueous solutions by synthesized Cu2+ and Sn4+ co-doped TiO2

The
communication has been addressed to the ejection of Ag (I) and Pb (II) from
aqueous solutions by Cu 2+-Sn4+/TiO2 nano
particles that are synthesized by Sol-Gel technique.
The  nano
particles are characterized by EDS,SEM, XRD, BET ,TEM, and FTIR analysis. Batch
experiments were done for various concentrations of 0.1 mg/L to 10 mg/L by taking Sorbent dose 1.5mg to study the adsorption
efficiency of heavy metal ions.

The
effect of different parameters such as initial concentration ,contact time, ,
pH and effect of coexisting ions on the adsorption of Ag(I) and Pb(II) were
investigated. Maximum sorption of 2.03 mg/g in case of Ag(I) and 1.84 mg/g in
case of Pb(II) was noticed from the solution of initial metal ion concentration
0.1 ppm, temperature of 323 K, pH 6, shaking time of 60 min Ag(I) and contact
time of 30 min Pb(II) Sorption. The adsorption kinetics was well fitted using a
pseudo-second order and Reichenberg kinetic model.  Langmuir and DR isotherms were found well
fitted with the data.  Sorption improved with increase in temperature
in the studied temperature range and endothermic. And the values of ?H°, ?S°
and ?G° were also evaluated. BET surface areas
of sorbent particles were 92.05m2/g. X-ray diffraction and high-resolution transmission electron microscopy
data revealed that the size of the sorbent particles was 14.21nm.

 

Key words: Kinetic data, Sorption
isotherms, Adsorption, Thermodynamic Parameters

 

1.      Introduction:

The
waste water, having numerous kinds of pollutants that are ejected from various
industries are contaminating the fresh water bodies posing a stern threst to
the environment and living organisms [Schwarzenbach, R. P.et
al 2010]. When compared to types of waste water
pollutants, heavy metals are the most significant ones, as they are very toxic
even at very low concentrations and are persistent in the environment which is
causing a life threatening problem to aquatic flora, fauna and its environment  [Seiler, H. G. et al .1988, Yadanaparthi, S. K. R.et al,2009]. Electroplating industry, tanneries, electronics
manufacturing industry, coal-fired power plants and mining operation are key
sources of heavy metal pollution in water. Thus before releasing these waste
waters from industries into freshwater bodies they must be treated well to
prevent the contamination by toxic metals. [Wang, J. & Chen ,2009, Yin, P.,2010 ]. automobile batteries, fuels, printing processes, photographic
materials, pigments, ceramic and glass industries release tremendous amounts
of  Lead (Pb(II)), a potentially toxic
metal ion that is being discharged into fresh water bodies making it unsuitable
for consumption. [Li, Y.-H. et al 2002,].
 Pb(II) is highly toxic to human beings
and biota even at trace concentrations. Exposure to high levels of Pb(II) shows
adverse  effects as it can  damAg(I)e the central nervous system and brain
and finally leads to death [Sanders, T.2009].
US Environmental Potential Ag(I)ency (US EPA) has set the maximum contaminant
level of Pb(II) in drinking water i.e 15 ?g L?1 [Agarawal, A.2005]. Most of the world’s silver is recovered from
scraps, such as photographic films, X-ray films, jewelry, electroplating, ink
formulation, mirroring, porcelain, and metal alloy industries. Due to its
unique nature of antibacterial and anti fungal properties, silver is  used especially  in washing machines, refrigerators, air
conditioners, air purifiers, and vacuum cleaners. As a result of which
industries produce wastewater contaminated with a significant amount of silver
[Atia, A. A ,2005, Lu, X.2010]

 precipitation, electrolysis, solvent
extraction, use of ion-exchange resins, chelating Ag(I)ents etc are the
currently available technologies for silver removal. These processes show
satisfying results when the concentrations in effluents are fairly high, i.e.,
above 100 ppm, [Murat A.,2006].

Silver
levels of less than 0.000001 mg silver per cubic meter of air ( mg/m3),
0.2-2 parts silver per billion parts water (Pb(II) in surface waters, such as
lakes and rivers, and 0.2-0.3 parts silver per million parts soil (ppm) in
soils are found from naturally occurring sources, [U.S. Public Health Service,
1990].

 It is imperative to develop techniques for
trapping heavy metals from water.[ F. Fu. 2012, Y. Li 2015, J. Feng 2013,Q.
Zhang 2013, Y. Huang 2015] several techniques have been proposed to remove
heavy metals from aqueous solutions including chemical precipitation, reverse
osmosis, membrane filtration, coaggulation, extraction electrochemical
treatment techniques, ion exchange,  irradiation, and adsorption.[
V. K. Gupta 2009, V. K. Gupta 2006, A. Heidari 2009, M. Xu 2011, F. Fu and Q
2011] Adsorption technique is the most
extensively used  compared to other
methods owing to its  low cost superior
properties, high efficiency, operation-easiness, and cost-effectiveness, which
make it an attractive approach for water treatment.[ V. K. Gupta 2012, K.
Zargoosh 2015, K. Kalantari 2014, V. Chandra 2010, D. Zamboulis 2011, L. Ma 2016]

Recently, nano material sorbents
have been extensively used as sorbents due to their higher adsorption
properties than bulk materials as they possess higher surface areas and more
surface active sites. [X. Wang,2012, P. Z. Ray 2015]

 Nano sized metal oxides as one of the
inorganic materials are used  largely for
heavy metal ion removal in wastewater treatment in recent decades as they have
specific affinity and exhibits minimal environmental impact and low solubility
with no secondary pollution.[ C. Gao 2008, J. Fabrega 2011]

 

Inorganic and organic pollutants from wastewater can be cheaply and
potentially removed by Titanium dioxide photo catalyst. transition metal ions
are doped with the titanium dioxide to enhance photo activity and shift of the
absorption spectrum to the visible region.

Titanium(IV) oxide (TiO2), an
important n-type semiconductor with a direct band gap of 3.2 eV, has also
received considerable attention mainly in environmental photo catalytic
processes such as splitting of water into H2 and O2,
removal of pollutants from air, water and solar cells [L. Etgar 2012, Q.
Xiang 2011, G. Wang 2011, J. Tang 2011, . S. Liu 2011].

In heavy metal removal the dopant ions can
function as both hole and electron traps or they can mediate interfacial charge
transfer. The extent of metal dispersion on the particle surface and chemical
composition homogeneity of a single particle depends markedly on the doping
methods and calcinations temperature, thus leading to different morphological and
crystalline properties [Zhang, R.,2004, Anpo, M et al.2000,] .
Instead of using high cost UV-illumination, the widely available solar
radiation makes photo catalytic process more attractive and provides a powerful
source for waste water pollutant elimination [Romero, M.,1999].

Although titania
catalysts have been extensively studied, the procedure of preparing photo
catalytic metal-doped titania is still of great interest. Particle size of
catalyst is considered one of the most important physical parameters in these
reactions, because it can directly furnish the active sites for the reaction to
occur [C. H. Cho 2003, Y. Oguri 1988, J. L. Look 1992].

In the present study the author has made an
attempt to synthesize Cu-Sn-TiO2 nano particles by adopting Sol-gel
method. The versatility of sol-gel chemistry provides a means of controlling
the shape, morphology and textural properties of the final materials [Rao, C.
N. R,2003]

The prepared Cu2+ and Sn4+
co-doped TiO2 photo catalyst was characterized by several analytical
techniques such as XRD, FTIR, FE-SEM, EDS, HR-TEM, BET  and SAED.

The synthesized oxide has been used for adsorption
studies of heavy metals such as Ag(I) (II) and Pb(II). Batch equilibrium experiments were performed for various
concentrations of 0.1 mg/L to 10 mg/L to study
the removal efficiency of heavy metal ions. The effect of different parameters
such as contact time, initial concentration, pH and effect of coexisting
substance on the adsorption process were investigated. The adsorption kinetics
were tried for pseudo-first order kinetic model, pseudo-second order kinetic
model & Elovich’s equation. Langmuir
Frendlich, Temkin and D-R isotherms studies are also performed. Weber-Morris
and Reichenberg Kinetic equations were employed to explain the diffusion
process.