Prantik Banerjee

We demonstrate a general single-pot heating method for preparing iron-doped zinc oxide nanocrystals from acetyl acetonate precursors in non-aqueous solvents. The particles were characterised by transmission electron microscopy (TEM), powder X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), UV-visible (UV-Vis) and Fourier transform infrared (FTIR) optical absorbance spectroscopies. The dependences of the size of the nanocrystals and doping level on the synthesis temperature and precursor composition were elucidated and modelled.

Multifunctional cotton fabric has been prepared by pad-dry-coating with sonochemically synthesized zinc oxide
nanoparticles. The uniqueness of sonochemical synthesis is that it synthesizes without alkali at near neutral pH and
hence the cotton fabric is exposed to less chemical stress. As a result of coating, the fabric shows enhanced mechanical
strength, water and stain repellence, antimicrobial properties, UV-blocking capacity and self-cleaning characteristics
compared to the uncoated fabric. The self-cleaning property was tested with Trypan Blue dye under sunlight. The
attempt of quantifying the self-cleaning process with the rate of decolorization is a novel one. It was observed that about
69% of the colour was removed when the coated fabric was exposed to sunlight for 3 h and 30 min. The fading of
colour followed pseudo-first-order kinetics.

ABSTRACT
Homogeneous Fenton reaction (Fe2+/H2O2) is one of the most important advanced oxidation
processes to generate
OH free radicals for degradation of organic pollutants in wastewater.
Degradation of an azo dye (Trypan Blue) by solar photo-Fenton process has been
investigated in this work using a batch reactor under sunlight. Instead of acidic pH used in
conventional Fenton reaction, neutral pH is used here to modify the same. Effects of the
changes in process parameters, including dosage of ferrous sulphate and hydrogen peroxide
as well as pH have been examined. Percent degradation was observed to increase with
increasing H2O2 dosing up to a particular critical value. Increase in FeSO4 dose and acidic
medium increased degradation. Complete decolourization was achieved after 2 h when
500 mL of 5.2 × 10−4 mol L−1 dye aqueous solution at pH 7 was oxidized with
2.8 × 10−4 mol L−1 of ferrous sulphate and 0.03 mol L−1 of H2O2 under sunlight of average
intensity 281 W m−2. Mineralization of dye pollutant was monitored by COD measurement.
Additionally, FTIR analysis also supported degradation. A kinetic model was developed
and validated with experimental data.

Abstract Azo dye and hexavalent chromium are two carcinogenic and toxic pollutants present in industrial wastewater. Zinc oxide nanoparticles can be used for the treatment of these pollutants with solar energy. However the nanoparticles themselves generally have some inherent toxicity for aquatic life. In this work, we have selected Channa punctatus as the model aquatic animal and examined whether the net toxicity to which it was exposed in wastewater before treatment, decreases after photocatalytic treatment of dye and hexavalent chromium using ZnO nanoparticles as photocatalyst under sunlight. Lipid Peroxidation (TBARS) and Reduced Glutathione (GSH) have been used as measures of toxicity in fish. We have compared these parameters under different experimental conditions comprising organic and heavy metal pollutants with and without nanoparticles.

Abstract The present study aims at searching the
potential of commercial grade steel wool in reducing
hexavalent chromium in aqueous phase under batch mode.
About 30 % of the initial hexavalent chromium was found
to reduce within 2 h at a pH of 3. However, on testing the
combined effects of different process parameters, namely
the solution pH, wool loading, etc., the optimum batch
parametric condition has been fixed. A moving boundary
type kinetic model, which takes into account the effect of
passivation along with the direct reduction mechanism to
simulate the gross uptake profile of Cr(VI) from the bulk
solution is proposed. The effective pore diffusivity of
Cr(VI) in commercial steel wool was determined by a
suitable global optimization technique. Additionally, the
model is also capable to simulate the decline of active
external surface area of the wool caused by passivation
with time. A good match of the experimental data and
model-simulated transient bulk concentration of Cr(VI)
(under optimum parametric condition only) establishes the
general validity of the proposed model.

ABSTRACT
Scarcities of water and energy are going to be critical in the near future. A possible remedy
is to reuse industrial wastewater after suitable treatment using a renewable energy. In this
work, wastewater containing hexavalent chromium is treated with Zinc oxide (ZnO) semiconductor
photocatalyst in the presence of sunlight to reduce the more toxic hexavalent
metal to its less toxic trivalent counterpart. Thirty five percent reduction was obtained after
2 h with 10 mg/L substrate, 0.4 g/L photocatalyst, and 75kLux solar radiation at 31oC temperature.
Process parameters are initial concentration of substrate, loading of photocatalyst,
pH and concentration of the electron donor. Initial rate of reduction varied only with ZnOloading
and hence it was zero order with respect to both the substrate and electron donor.
An alternative rate equation based on the modified Langmuir Hinshelwood Hougen Watson
(LHHW) model compares well with the mechanistic rate equation.

Hexavalent chromium is more toxic and carcinogenic compared to its trivalent counterpart. Hexavalent
chromium can be photocatalytically reduced to trivalent one using zinc oxide semiconductor and solar
or UV radiation as light source. But an important ecological aspect is whether the net toxicity decreases
after the photocatalytic process. In the present work, we have selected Anabaena flos-aquae as the
model organism and examined whether the net toxicity to which it has been exposed in water
decreases after photocatalytic reduction of hexavalent chromium using ZnO semiconductor as
photocatalyst. We have studied the cumulative toxicities of both chromium (before and after
treatment) and ZnO (both nano and micro) separately and as a suspension of ZnO in chromium.
Quantitative cell surface roughness analysis was conducted using AFM to confirm the changes in cell
surface properties.

Abstract Heterogeneous semiconductor photocatalysis is a versatile technique for pollution control of air, water, and plastic. It degrades organic pollutants nonspecifically to carbon dioxide and water, reduces carbon dioxide to organic molecules, and generates the clean fuel hydrogen by splitting water. Though titanium dioxide (TiO2) is the most popular photocatalyst, zinc oxide (ZnO) has got a few advantages. Especially for solar or visible light photocatalysis, ZnO serves better. ZnO-based nanomaterials have been utilized for the treatment of polluted air, wastewater, and plastic under both artificial UV light and sunlight. This chapter includes a review on the various environmental applications of ZnO-based nanophotocatalysts with its synthesis and characterization. There are several methods of synthesis, including sol–gel, sputtering, vapor deposition, and microwave or ultrasound-assisted ones. Characterizations are done by microscopic and spectroscopic techniques along with physical methods. There are different types of ZnO-based nanophotocatalysts such as immobilized, doped, and composite ones. Basic mechanistic steps as well as photoreactors are discussed. Ecotoxicity of the nanostructures is elaborated for awareness before applying nanoparticles for the environment. For the crisis of energy and environment, ZnO-based nanostructures may offer a solution through solar photocatalysis.

Sonochemically synthesized zinc oxide (ZnO) nanoparticles were coated on paper for enhancing its properties in view of the preservation of documents. The paper used for accession register was used as substrate. Physical, chemical, optical, hydrophobic, and antifungal properties of the coated and uncoated papers were compared. Nanoparticles were synthesized with ultrasound from organic precursors and were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), whereas coated and uncoated papers were examined following standard procedures as described by the Bureau of Indian Standards (BIS). It was observed that coating with nanoparticles imparted mechanical strength, water repellence, and antifungal properties to the paper without compromising its printability. Hence, coated paper is comparatively more suitable for preservation of written or printed documents than uncoated paper.

Hexavalent chromium in industrial wastewaters mainly originates from tanning, painting and metal processing industries. Highly mobile chromium (VI) compounds are toxic as well as carcinogenic and mutagenic even at low concentrations whereas its trivalent counterpart is less mobile, non-carcinogenic and less toxic. Advanced oxidation processes (AOP) like photocatalytic reduction of Cr(VI) in aqueous suspensions of semiconductors such as TiO 2 , ZnO, CdS, ZnS, and WO 3 under UV illumination has also been widely studied. In the present work laboratory grade ZnO has been used as a semiconductor catalyst to reduce hexavalent chromium present in potassium dichromate under solar irradiation. The sacrificial electron donor used was methanol. Adsorption of dichromate on the ZnO particles was found to be negligible. Though the extent of photoreduction was found to decrease with increasing initial concentration of dichromate solution, the initial rates were found to be nearly independent to th...

Wastewater from textile, paper, and some other industries contain residual dyes, which are toxic as well as aesthetically displeasing and are not readily biodegradable. Advanced Oxidation Processes (AOPs) involving UV radiation, Fe 2+ ion and H 2 O 2 are alternative techniques of destruction of dyes and many other organics in wastewater. Semiconductor photocatalysis is one of such AOPs, which can be conveniently applied for degradation of dye pollutants with complete destruction of it to carbon dioxide and water. In the present work, photocatalytic degradation of Trypan Blue, a dis-azo dye (CI no.23850), has been explored in aqueous solution, using ZnO-nanoparticles as catalyst and solar light as the source of energy for photo-excitation. The influences of process parameters such as photocatalyst loading and initial dye concentration have been investigated. COD values were also measured before and after photocatalysis and COD removal percentages were calculated. Decolourisation with...

Wastewater from the industries like textile, leather and paper is often contaminated with dye pollutants. Though azo-dyes are banned in developed countries, the directive is not totally implemented in the developing countries. Various techniques have been developed over the years to remove the dye-pollutant from wastewater. Advanced Oxidation Processes (AOPs) involving the generation of hydroxyl radical is one of such techniques which breaks down the organic pollutant to carbon dioxide and water. Fenton and photo-Fenton oxidation reaction, O 3 /UV, H 2 O 2 /UV are some of the AOPs. Among the AOPs, semiconductor photocatalysis involves a catalyst and a source of energy for excitation of the same. In tropical countries like India, solar energy can be employed as the source of energy in photocatalytic degradation of dyes to make the process economically attractive and environmentally benign. In the present research, we have used three varieties of ZnO nanoparticles, sonochemically synt...

Hexavalent chromium is more toxic and carcinogenic compared to its trivalent counterpart. Hexavalent chromium can be photocatalytically reduced to trivalent one using zinc oxide semiconductor and solar or UV radiation as light source. But an important ecological aspect is whether the net toxicity decreases after the photocatalytic process. In the present work, we have selected Anabaena flos-aquae as the model organism and examined whether the net toxicity to which it has been exposed in water decreases after photocatalytic reduction of hexavalent chromium using ZnO semiconductor as photocatalyst. We have studied the cumulative toxicities of both chromium (before and after treatment) and ZnO (both nano and micro) separately and as a suspension of ZnO in chromium. Quantitative cell surface roughness analysis was conducted using AFM to confirm the changes in cell surface properties.

Common sources of chromium in wastewater are leather industries, elec-troplating, electronic, and timber. Hexavalent chromium is more toxic and carcinogenic than trivalent chromium. Photocatalytic reduction of Cr (VI) to Cr (III) in an aqueous medium under tropical sunlight and nanosized ZnO semiconductor catalyst has been investigated using potassium dichro-mate as the model compound. Methanol was added as a hole-scavenger for enhancement of the photo-reduction. Effects of the process param-eters such as nano-ZnO loading (0 to 0.6g/L), initial concentration of sub-strate solution (10 to 50mg/L), pH (4-9) and methanol-dosing (0 – 1.75mol/ L) have been investigated. The initial rate of the photochemical method was found to be independent of the concentration of potassium dichro-mate as well as concentration of methanol above an optimum value. A probable mechanism for the entire reaction and the corresponding kinetic model have been proposed for the photo reduction and proved by exper...