Remediation for Heavy Metal Contamination 283
Table 16.4. Chemically synthesized nanomaterials used for detecting heavy metals.
Nanomaterials
Method of detection
Metals
References
BiNPs
Electrochemical
Ni2+, Pb2+ and Cd2+
Niu et al. 2015
Graphene/CeO2
Electrochemical
Cd2+, Pb2+, Cu2+, and Hg2+
Xie et al. 2015
Core-shell SiO@Ag NPs
Colorimetric
Hg2+
Boken and Kumar 2014
Carbon xerogel BiNPs
Electrochemical
Pb2+ and Cd2+
Gich et al. 2013
GQDs functionalized AuNPS
Electrochemical
Hg2+ and Cu2+
Ting et al. 2015
16.3.1.4 Field-effect Transistor (FET) Sensors
Heavy metals have been detected using FET sensors that take advantage of the interaction between
the analyte and the semiconductor resistance (Chen et al. 2011). The conductivity variations caused
by the selective redox interaction between single-walled carbon nanotubes (SWCNTs) and Hg2+
have been used to create a FET sensor (Kim et al. 2009). In both drinking water and aqueous
solution, this sensor demonstrated a broad detection limit from 10 nM to 1 mM, as well as high
selectivity for Hg2+ over the other metal ions.
16.4 Application of Nanomaterials for Decontamination of Heavy Metals
Heavy metals and metalloids (viz., Pb, Cd, Fe, Se, Ni, Cu, Co, As, etc.) are hazardous and persistent.
Recent advances in nanotechnology have prepared the path for novel approaches to heavy metal
remediation, particularly in wastewater treatment, where nanomaterials are used in water purification
via mechanisms such as adsorption and degradation of toxic materials. According to research,
nanoparticles can assist in reducing the adverse effects or absorption/uptake of heavy metals.
A study was conducted to evaluate how nano-TiO2 (2–6 nm) can reduce the effect of wastewater
(containing heavy metals) on the development of maize seedlings. Analysis of wastewater revealed
that it was unfit for irrigation as it contained high levels of heavy metals (Zn, Cu, Fe, Mn, Cr and Cd)
beyond the permissible levels for irrigation. During in vitro studies, the nano-TiO2 suspension was
administered at different concentrations, either autoclaved wastewater or deionized water. Nano
TiO2 at a concentration of 25 mg L–1 significantly reduced the negative effects of wastewater on
maize development indices (Yaqoob et al. 2018). Further, the effects of nano-Fe3O4 in reducing
heavy metal toxicity in wheat seedlings were investigated by Konate et al. (2017). The use of nano
Fe3O4 (@2000 mg L–1) in a 1 Mm solution dramatically reduced the negative impact of heavy metals
on the growth in wheat seedlings. The beneficial impacts of nano-Fe3O4 under heavy metal stress
might be due to increased antioxidant enzyme activity (Konate et al. 2017). Praveen et al. (2018)
reported the effectiveness of iron oxide nanoparticles (Fe3O4 NP) in dropping detrimental effects
of As in Brassica juncea. They also reported that the application of Fe3O4 NP further decreased the
stress in plants induced by As contamination. Under cadmium stress, zinc oxide nanoparticles were
found to improve wheat chlorophyll content, gas exchange characteristics, antioxidant enzymes,
zinc absorption and yield while lowering Cd concentration. Siddiqui and Al-Whaibi (2014)
discovered that 8 g L–1 of 12 nm nano-silicon oxide increased seed germination in Lycopersicum
esculentum. It has also been observed that nanostructured silicon dioxide aids in the reduction of
plant transpiration rates, as well as the improvement of the plant’s green color and shoot growth.
Application of nano SiO2 reduced As uptake in rice seedling through improving pectin synthesis
and the mechanical force of the cell wall. Recently, various iron nano-materials have been employed
to minimize heavy metal uptake in plants. In the modern era, the application of nanoparticles not
only reduces the uptake of heavy metals in plants but also decontaminates the environment through
different mechanisms. Next the different applications of nanomaterials (viz., photocatalyst, nano
absorbents, nano clay polymers, etc.) to reduce the heavy metal burden in the environment are
described.