Synthesis of Nanoporous Materials for Abatement of Inorganic and Organic Contaminants in Water

Abstract

Increase in water pollutants make water unfit for drinking purposes as well as for irrigation purposes. Moreover, consumption of contaminated water leads to various health issues,motivating us to carry out the present study. This dissertation focusses on the remediation of water pollutants by designing suitable materials. To achieve the main aim, there are two objectives: 1) removal of inorganic contaminants using nanoporous metal oxide materials
synthesized via imidazolium-based ionic liquids as a novel media and 2) remediation of organic pollutants by photodegradation method using biodegradable nanocomposite
catalysts. Several techniques were applied for the removal of inorganic contaminants so far. Among them adsorption techniques with suitable adsorbent has been an efficient method. In the first project, we used room temperature imidazolium-based ILs for the synthesis of
mesoporous silica via sol-gel method and used as an efficient adsorbent for the removal of lead from synthetic aqueous solution. The results revealed that the mesoporous silica synthesized using ILs having higher alkyl chain results greater affinity towards lead ions. The maximum removal of Pb(II) was 5.18 mg g􀀀1 at the optimum condition of 0.7 g of silica adsorbent, pH of 6 and at 40◦C. The equilibrium data of Pb(II) were best described by Freundlich adsorption isotherm. The adsorption kinetics of Pb(II) were found to follow the pseudo-second-order kinetic model. In the same direction, in the second project, 1-methyl-3-octylimidazolium chloride ILs modified alumina was prepared via sol-gel route and used as a novel adsorbent for de-fluoridation from synthetic as well as from real contaminated water collected from Boden block of Odisha state. Experimental results showed that the prepared material works very well for practical purpose. The IL modified γ-alumina acts as a good adsorbent for fluoride ions due to interesting interactions such as electrostatic interaction and ion exchange process. Adsorption kinetic study showed that the adsorption process followed the pseudo-second-order kinetics and the maximum adsorption
capacity is found to be 25.0 mg g􀀀1 from Langmuir adsorption isotherm. Fixed bed column study was carried out to check the role of flow rates on adsorption of fluoride ions using synthetic and contaminated aqueous solution. For the removal of orgasnic pollutants, in the third project titania coated silica nanoparticle was synthesized via nanoparticle encapsulation method and was used for the photodegradation of safranin-O dye from aqueous solution under UV light irradiation. The synthesized material was characterized by FT-IR, XRD, FESEM, N2 adsorption-desorption method and Zeta potential measurements. The TEM
results showed that the nanoparticles have a core-shell structure composed of about 100 vii nm of diameter of silica with several TiO2 fine particles in shell. Afterdegradation, this process was optimized through the response surface methodology (RSM). In this response study, photodegradation efficiency was evaluated by three main independent parameters such as catalyst dose, initial dye concentration and reaction time. Parameter sensitivity studies of the degradation efficiency of titania coated silica nanoparticles have shown 93.29% degraded under the optimal conditions of catalyst dose of 89.80 mg g􀀀1, initial dye concentration of 17.61 mgL􀀀1 and reaction time of 12 min. We cross-checked the predicted values of degradation efficiency with the experimental values and these found to be in good agreement(R2 = 0.9983 and adj-R2 = 0.9967). In the forth project, we further extended this process
to degrade phenol and its derivatives by using biodegradable material. In this contest, HAp-ZrO2 nanocomposite was synthesized via sonochemical method. It was found that the zirconia nanoparticles were uniformly distributed on the surface of hydroxyapatite with mean size of 10±5 nm. The obtained HAp-ZrO2 material was used as a photocatalyst for degradation of phenol, 4-nitrophenol and 4-chlorophenol. Results showed that the material had higher degradation efficiency towards phenol, followed by 4-chlorophenol and 4-nitrophenol. Presence of various functional groups and high reactive atoms on the HAp-ZrO2 made it an efficient photocatalyst for degradation of phenol and its derivatives. All of the results suggested that the above said materials have a strong and specific affinity towards the inorganic and organic contaminants, and can be considered as excellent material for treatment of real contaminated water system.