Doctor of Philosophy Chemistry - ethesis

This is to certify that the work presented in the thesis entitled DEVELOPMENT OF NEW ENVIRONMENTALLY FRIENDLY ADSORPTION MEDIA FOR THE REMOVAL OF HAZARDOUS ANIONS FROM WATER, submitted by TAPASWINI PADHI (Roll No.509CY607) to National Institute of Technology, Rourkela, is a record of bonafide research carried out by her under my supervision and guidance in partial fulfillment of the requirement of the degree of Doctor of Philosophy in Chemistry. The maximum adsorption capacity of the material for fluoride was found to be 103.9 mg g-1 with the optimum condition.

Background of the Study
Sources of Fluoride and Arsenic in water and their toxicity

Fluoride
Arsenic

Processes for the separation of Fluoride and Arsenic from contaminated water

Adsorption

Scope of Study

Adsorbents used for removal of Fluoride and Arsenic

Organization of Thesis

In some places in Bangladesh, arsenic concentrations are reported to be as high as 1mgL-1 (Harvey et al. 2002). Due to its simplicity of design and operation, adsorption has been proven to be a better process for water treatment (Lafrano et al. 2012).

Mixed oxide nanoparticle

Remediation of selected anions from aqueous media

Magnetic chitosan nanoparticle

Remediation of selected anions from aqueous media

Mesoporous materials

Summary of Previous Work

Layered double hydroxide

Summary of Previous Work

Research Gap
Research Objective

Thus, the chemical modification of the surface improves the removal capacity of toxic anions in the water treatment process (Mahmood et al. 2013). Zhang et al. (2016) synthesized Fe3O4 magnetic nanoparticles coated with Fe-Ti bimetal oxide by co-precipitation method and found that the saturation fluoride adsorption capacity was 57.22 mg/g.

Reagents and Chemical
Adsorbate preparation
Adsorbent preparation

Synthesis of Fe-Al mixed oxide nanoparticle
Synthesis of magnetic chitosan nanoparticle
Synthesis of Lanthanum based Zirconium phosphate (La-ZrP)
Synthesis of Mg/Fe-CO 3 LDH

Characterization of the adsorbent

Zero point charge (pH ZPC )
X-ray diffraction study (XRD)
Scanning electron microscopy (SEM)
Transmission electron microscopy (TEM)
Fourier transforms infrared spectroscopy (FTIR)
Brunauer-Emmett-Teller (BET) analysis
Thermogravimetric analysis (TGA-DTA)
Atomic absorption spectrometer (AAS)

Batch adsorption study

Adsorption study
Desorption Study
Reuse Study

Adsorption kinetic models

Kinetic Model (pseudo 1 st order)
Kinetic Model (pseudo 2 nd order)

Adsorption isotherm study

Langmuir isotherm model
Isotherm model (Freundlich)

Thermodynamic study
Column adsorption studies

It can be defined as the pH at which the charge of the adsorbing surface is zero. The change in frequency thus provides information about the interaction between the surface molecules and the nanoparticles (Zhang, 2009). Calculation of the amount of adsorbed N2 gas physically corresponds to a monolayer coverage, which determines the specific surface area of the adsorbent.

Any physical or chemical change occurs due to a change in the heat contained in the material. A kinetics study is performed to evaluate the mechanism and the rate-determining step of adsorption. Therefore, it is possible to calculate qe and Ks from the slope and intercept of the graph between t/qt as a function of t.

The column was then filled with the required amount of the adsorbent to achieve the required bed height.

Introduction

Results and Discussions

Characterization
Surface Morphology
TEM analysis
XRD analysis
Thermal (TGA/DTA) analysis
FTIR study
BET Isothermic analysis

Sorption studies

Effect of dose
Effect of pH
Effect of initial fluoride concentration
Adsorption isotherm
Effect of contact time
Effect of temperature and thermodynamic study
Effect of competitive ions
Regeneration study

Column study

Flow rate effect on breakthrough
Initial fluoride concentration effect on breakthrough
Adsorbent mass (bed height) variation study on breakthrough

Chapter summary

Introduction

Agarwal et al. 1999) and the risk of high fluoride dosage (Hichour et al. 2000) have previously been studied in the literature. In the field of water treatment, the use of nanoparticles becomes difficult due to complicated separation process, but in the case of magnetic nanoparticles, the separation is very easy by applying magnetic field. Magnetic nanoparticles are therefore considered to be effective adsorbents compared to other nanoparticles (Murray et al. 1999) in terms of environmental impact, chemical stability and cost and maintenance.

The aim of this study was to investigate the potential of co-removal of fluoride with magnetic chitosan nanoparticles.

Results and Discussions

Characterisation
XRD Analysis
FTIR Analysis
SEM Analysis
Magnetic Property

The analysis revealed that the bare synthesized Fe3O4 nanoparticle was pure magnetite and the chitosan coating process resulted in several phase changes resulting in a mixture of magnetite, goethite and iron oxide-hydroxide. The FTIR spectra of bare Fe3O4 nanoparticles, Ch-Fe3O4 nanoparticles, and glutaraldehyde-linked Ch-Fe3O4 nanoparticles were examined to realize the bonding mechanism as shown in Figure 5.2. The SEM micrograph of cross-linked Ch-Fe3O4 [Figure 5.3(b)] presented relatively compact surfaces and some macropores.

However, with the introduction of Fe3O4 nanoparticles into chitosan by microemulsion process, there was remarkable change on the surface morphology of crosslinked Ch-Fe3O4 nanoparticle [Figure 5.3(b)]. The SEM micrograph of both the samples indicated that the particle size of Ch-Fe3O4. For Fe3O4 nanoparticle, an unsaturated hysteresis loop was obtained with application of magnetic field (1.5 T) indicating strong magnetic behavior (Yogi and Varshney, 2013).

Thus, Chitosan present in Ch-Fe3O4 induced complete orientation of magnetic domain in stable Fe3O4.

Sorption Studies

Adsorbent dose variation
Effect of pH
Kinetic Study
Temperature variation

Synthesis of Chitosan Encapsulated Magnetic Nanoparticles and Its Application for Fluoride Removal from Water. There was an increase in percent fluoride removal with increasing pH ranging from 2-8, after which percent removal decreased. The adsorption removal rate of fluorine from Ch-Fe3O4 nanoparticle was investigated with the help of pseudo first order and pseudo second order equation (Figure 5.7).

The removal rate increased with increasing time to 83.8% and approached equilibrium within 120 minutes due to occupation of adsorption adsorption sites in the adsorbent surface at higher fluoride concentration. The parameters obtained from both kinetic models are given in Table 5.1, showing that the adsorption rate better fit the pseudo 2nd order kinetic model (R2=1). In the current study, the adsorption process was analyzed using Langmuir (Figure 5.9) and Freundlich isotherm models.

The parameters calculated from the Langmuir equation showed RL = 0.0644 indicating favorable adsorption and qmax = 33.62 mg/gm.

Column Studies

Effect of flow rate on breakthrough
Initial fluoride concentration variation effect on breakthrough
Aadsorbent mass variation study on breakthrough
Application of Bed depth service time (BDST) model

Results of the sorption process by the Ch-Fe3O4 nanoparticle with variation of flow rate, initial concentration and bed mass/height on the sorption performance of hybrid material are presented in the form of breakthrough curves (BTC). Considering the maximum allowable concentration of fluoride as 1.5mg/L, the breakthrough time for the above flow rates was 10, 4 and 2 hours respectively. This phenomenon is due to reduction in contact time between the adsorbent F and the adsorption media leading to rapid approach to the 10 mg/L initial concentration.

The time of breakthrough decreased with increasing concentration of fluoride and was found to be 5, 12 and 16 hours for concentration of (15, 10 and 5 mg/l), respectively (Figure 5.12). The rate of adsorption was affected by the initial adsorbate concentration of a solute during the course of adsorption due to unavailability of the active sites. The theoretical depth of adsorbent required to prevent the concentration of adsorbate from exceeding the maximum allowable concentration limit is represented by bed depth Cb.

The slope of the BDST plot (Figure 5.14) gives the time required for the adsorbate solution to cross a unit length through the adsorbent bed with certain experimental conditions at a certain adsorbate concentration.

Chapter Summary

The K value determines the rate of transfer of adsorbate mass from the liquid phase to the solid phase (adsorbent bed). SEM, XRD and IR studies show that the cross-linking of Fe3O4 with Chitosan resulted in the formation of a larger particle size compared to bare Fe3O4, indicating the encapsulation of Fe3O4 with Chitosan. The adsorption rate was well fitted to pseudo second-order kinetics and the process obeyed the Langmuir isotherm model.

The column study shows that the synthesized adsorbent is capable of lowering the fluoride concentration to an acceptable limit (1.5 mg/l).

Introduction
Results and Discussions

Characterisation
XRD Analysis
Thermal Analysis
FTIR Analysis
SEM study
BET surface analysis

Sorption studies

Effect of adsorbent dose
Effect of pH
Mechanism of adsorption
Kinetics of Adsorption

Effect of temperature

Regeneration-Reuse Studies
Effect of interfering ions

Column Study

Effect of initial fluoride concentration on breakthrough
Adsorbent mass/bed variation on height on breakthrough

Chapter Summary

Thus, the present work is focused on the synthesis and characterization of mesoporous La-ZrP by FTIR, XRD, SEM to study its fluoride removal efficiency. The pHZPC of mesoporous La-ZrP was found to be 6.8 and the particle size was 186 nm. The FTIR shown in Figure 6.3 shows the complete removal of surfactant from La-ZrP by calcination at 500 °C.

The fluoride removal efficiency of La-ZrP was performed with variation of dose at contact time two hours and initial concentration 10 mg/l. Since the pHZPC of mesoporous La-ZrP was calculated to be 6.8, the favorable pH for adsorption is 6.5~7. Decontamination of fluoride with mesoporous La-ZrP was thus cost-effective to reach the maximum allowable limit of fluoride in water.

The mesoporous La-ZrP compound was successfully used for fluoride removal using fixed-bed columns.

Introduction
Results and Discussions

Characterisation
XRD Analysis
Morphological Analysis
BET analysis

Sorption Study

Adsorption Kinetics
Adsorption Isotherm

Column Study

Initial As(V) concentration variation study on breakthrough
Adsorbent mass (bed height) variation study on breakthrough

Chapter Summary

The calculated Mg/Fe molar ratios of the synthesized samples are roughly similar to the amount added during preparation. Weak peaks (inset of Figure 7.1) can be attributed to facets attached to the intralayer structure. SEM images (Figure 7.2a and 7.2b) show the presence of circular nanoplates in Mg3Fe synthesis. Figure 7.2c and d) shows the front and side view of the sample, which calculates the diameter and thickness of the nanoplates to be 300 nm and 30 nm, respectively.

The correlation between the As(V) adsorption capacity of the calcined LDHs with BET surface area is given in Table 7.2. The correlation coefficient of linear plot for the pseudo 2nd order kinetic model (inset in Figure 7.4) for all three LDHs approaches 1 (Table 7.3), indicating that the adsorption kinetics is best described by the pseudo 2nd order rate equation. SEM micrograph of the calcined Mg4Fe LDHs after adsorption clearly shows new phases in addition to hydrotalcite-like structures (Figure 7.6b).

The XRD patterns of calcined LDHs are given in Figure 7.6d, in which the pattern for Mg4Fe showed a new phase indexable to FeAsO4 (JCPDS No. 11-0048).

Conclusion

Quantitative desorption of fluoride from the adsorbent was found to be more than 93% at pH 7. The iron-aluminium (Fe-Al) mixed oxide nanoparticle was used in the defluorination of water using fixed bed columns. The nature of the breakthrough was influenced by the flow rate, the height of the column bed and the initial fluoride concentration.

Adsorption kinetics and isotherm of fluoride removal from aqueous synthetic solution were investigated by batch model as a function of adsorbent dose, solution pH, contact time, initial fluoride and temperature. The amount of fluoride removal increases with time and reached a saturation level at 120 minutes, and 93.0% of fluoride removal was achieved. The iron oxide nanoparticles can be used as an effective adsorbent for fluoride decontamination of water.

The Ch-Fe3O4 nanoparticle was successfully used for fluoride decontamination using fixed bed columns, and the breakthrough was affected by the bed mass, the initial concentration of fluoride and the flow rate.

Scope for Future Research

Asgari, B. and Bowen, J., 2017, "Gallium (III) metalloporphyrin grafted magnetite nanoparticles for fluoride removal from aqueous solutions". Islam, M., and Patel, R.K., 2007, "Evaluation of the removal efficiency of fluoride from aqueous solution using quicklime". Ku, Y., and Chiou, H.M., 2006, "The adsorption of fluoride ion from aqueous solution of activated alumina groundwater by electrodialysis: continuous operation".

Sari, A., and Tuzen, M., 2008, “Biosorption of Pb(II) and Cd(II) from aqueous solution using green alga (Ulva lactuca) biomass. Tomar, V., Prasad, S., and Kumar, D., 2014, "Adsorptive removal of fluoride from aqueous media using Citrus Limonum (Lemon) leaves". Waghmare, S.S., and Arfin, T., 2015, "Removal of fluoride from water by mixed metal oxide adsorbent materials: a review of the state of the art".

Wei, X., and Viadero, R.C., 2007, "Synthesis of Magnetic Nanoparticles with Ferric Iron Recovered from Acid Mine Drainage".