Title Page 1

Abstract 6

Contents 10

Abbreviations and symbols 23

CHAPTER 1. General introduction of the non-thermal plasma 25

1.1. General introduction 26

1.2. Paschen's law for breakdown voltage 31

1.3. Plasma-assisted environmental remediation 32

1.4. Plasma-assisted synthesis and applications of metal-based nonoparticles 34

1.5. Objective of study 36

CHAPTER 2. Plasma diagnosis and plasma-generated reactive species analysis 38

2.1. Experimental setup for multi-electrode dielectric barrier discharge plasma 39

2.2. Experimental framework for plasma jet 40

2.3. Electrical properties of dielectric barrier discharge plasma 41

2.4. Optical emission spectroscopy analysis 43

2.5. Electron temperature and density measurement 44

2.5.1. Collisional radiative model for argon gas 44

2.5.2. Collisional radiative model for nitrogen gas 47

2.5.3. Calculation of electron density for plasma jet 48

2.6. Calculation of vibrational temperature (Tᵥ) 50

2.7. Calculation of rotational temperature (Tᵣ) 52

2.8. Calculation of plasma frequency, Debye Length, and electric field within Debye sphere 53

2.9. Quantification of reactive oxygen and nitrogen species concentration in plasma generated gas 54

2.10. Quantification of reactive oxygen and nitrogen species concentration in liquid 55

2.10.1. Quantification of hydroxyl (OH') radical 56

2.10.2. Quantification of hydrogen peroxide (H₂O₂) 58

2.10.3. Quantification of nitrite (NO₂⁻) 60

2.11. Assessing physicochemical properties of plasma activated water 62

2.11.1. Measurement of pH 62

2.11.2. Measurement of electrical conductivity 63

2.11.3. Measurement of oxidation reduction potential 64

2.12. Statistical analysis 64

CHAPTER 3. Multi-electrode dielectric barrier discharge plasma for remediation of diesel-contaminated soil 66

3.1. Introduction 66

3.2. Experimental setup, instruments, and methodology 68

3.2.1. Plasma configuration 68

3.2.2. Plasma installation setup and layout 68

3.2.3. Soil preparation and removal analysis 70

3.2.4. Gas chromatography-flame ionization detection analysis 71

3.2.5. Phytotoxicity evaluation 71

3.2.6. Colony-forming unit (CFU) assay 72

3.2.7. Cell viability 73

3.2.8. Flow cytometry analysis 73

3.3. Result and discussion 74

3.3.1. Electrical and optical properties 74

3.3.2. Thermal properties 74

3.3.3. Measurement of gas phase reactive oxygen and nitrogen species concentration 76

3.3.4. Soil's morphological investigation 77

3.3.5. Variation of input power on diesel removal efficiency 79

3.3.6. Effect of input power on soil moisture for diesel contaminated soil removal 79

3.3.7. Variation of soil pH with removal efficiency 80

3.3.8. Impact of central ozone and nitrogen oxides generation on diesel contaminated soil 81

3.3.9. Analysis of diesel contaminated soil cleanup 83

3.3.10. Plasma-assisted diesel fuel removal mechanism 84

3.3.11. Test for the toxicity of diesel contaminated soil-phytotoxicity 85

3.3.12. Test for the toxicity of diesel contaminated soil -microbial toxicity 87

3.3.13. Test for the toxicity of diesel contaminated soil -normal human cell cytotoxicity 88

3.4. Conclusion 88

CHAPTER 4. Evaluating the efficacy of argon and air-mixed argon plasma jets for degradation of 4-nitrophenol 90

4.1. Introduction 91

4.2. Material and methods 92

4.2.1. Materials 92

4.2.2. Plasma setup and design 92

4.2.3. 4-nitrophenol degradation evaluation 94

4.2.4. Phytotoxicity assessment 95

4.3. Results 95

4.3.1. Electrical and optical analysis of argon and argon-air plasma jets 95

4.3.2. Evaluation of reactive oxygen and nitrogen species and physicochemical properties 98

4.3.3. Investigation of argon and argon-air plasma jet on 4-nitrophenol elimination 102

4.3.4. 4-nitrophenol degradation mechanism with argon and argon-air plasma jets 105

4.3.5. Microbial assessment 106

4.3.6. Phytotoxicity assessment 108

4.4. Conclusion 109

CHAPTER 5. Plasma remediation for synthetic textile dye-contaminated water: Effect of ozone and nitric oxide 111

5.1. Introduction 112

5.2. Materials and methods 113

5.2.1. Materials 113

5.2.2. Plasma configuration and setup 113

5.2.3. Raman analysis 113

5.3. Results and discussion 114

5.3.1. Plasma diagnosis 114

5.3.2. Analysis of plasma-generated reactive species 116

5.3.3. Plasma regulated dyes degradation analysis 120

5.3.4. Ozone generator plasma degradation mechanism for dyes 122

5.4. Conclusion 128

CHAPTER 6. Characterization of chitosan-functionalized gold nanoparticles via non-thermal plasma jet 130

6.1. Introduction 131

6.2. Experimental section, materials, and methods 132

6.2.1. Non-thermal plasma jet configuration and diagnosis technique 132

6.2.2. Materials 133

6.2.3. Non-thermal plasma synthesis of chitosan-functionalized gold nanoparticles 133

6.2.4. Chitosan-functionalized gold nanoparticles characterization 134

6.3. Results and discussion 134

6.3.1. Non-thermal plasma diagnosis for chitosan-functionalized gold nanoparticles synthesis 134

6.3.2. Assessing reactive species and physicochemical properties in plasma activated water 136

6.3.3. Optical and structural properties of non-thermal plasma generated chitosan functionalized gold nanoparticles 139

6.3.4. Morphological analysis of plasma-generated chitosan functionalized gold nanoparticles 143

6.3.5. Proposed reaction mechanism for the plasma-assisted synthesis of chitosan functionalized gold nanoparticles 146

6.4. Conclusion 148

CHAPTER 7. Impact of plasma plume length on the structural, optical, and dye degradation properties of citrate-stabilized silver nanoparticles 149

7.1. Introduction 150

7.2. Experimental methods 151

7.2.1. Plasma device setup 151

7.2.2. Electrical properties of plasma 152

7.2.3. Plasma synthesis of silver nanoparticles procedure 153

7.2.4. Structural and optical characterizations 154

7.2.5. Dye degradation procedure 154

7.3. Result and discussion 155

7.3.1. Optical characterizations of plasma jet 155

7.3.2. Physicochemical properties of plasma-treated silver precursor solutions 156

7.3.3. Structural and optical properties of silver nanoparticles 159

7.3.4. Plasma synthesis routes of silver nanoparticles 163

7.3.5. Degradation activity of methylene blue dye using plasma-synthesized silver nanoparticles 166

7.4. Conclusions 168

CHAPTER 8. Conclusion and Outlook 170

8.1. Conclusions 171

8.2. Future scope 173

References 175

Curriculum Vitae 190

Table 3.1. Comparing plasma cleaning methods for soil contaminated by petroleum 67

Table 3.2. Changes in soil moisture pre- and post-plasma exposure 80

Table 4.3. Comparing energy efficiency and kinetic parameters in synthetic dyes... 127

Plasma, considered as the fourth state of matter, provides a better way to tackle environmental pollution problems and is also capable of revolutionizing the synthesis of nanoparticles or NPs. This study deals with the various capabilities of multi-electrode dielectric barrier discharge (MEDBD) plasma and non-thermal plasma (NTP) jet for environmental remediation and green synthesis of metallic NPs. Plasma sources of the MEDBD type provide better control and enhanced utilization, and therefore would be useful in various pollutant abatement. Furthermore, it is also possible to focus on the synthesis of metal NPs which include silver (Ag) and gold (Au) using NTP jets. These jets are used to offer a controlled flow of gases for creating NPs with size and shape of the particles and change to near surface properties. In the overall, this study seeks to improve the efficiency of plasma technology for green and sustainable environmental remediation techniques applied in cleaning up the environment and the synthesis of green metallic NPs applicable in the environmental and biomedical sectors.

The first study showed the effectiveness of MEDBD plasma in cleaning diesel contaminated soil (DCS) through diesel removal from the soil. This study showed that MEDBD plasma had the potential to remove diesel pollutants present in the DCS at an efficient rate. To analysis and quantify the amount of diesel fuel before and after plasma treatment, a gas chromatography-flame ionization (GC-FID) detector was used. Assessment involved the varying soil pH and moisture, plasma dissipated power variation, and discharge quantities and concentrations of the specific reactive species O₃ (ozone) and NOₓ (nitrogen oxides). Using just 30 W of plasma dissipated power, the MEDBD system achieved an impressive 94.19% diesel removal in 60 min, with an energy efficiency of 1.78 × 10⁻²m³kW⁻¹h⁻¹. O₃ was the most effective plasma produced reactive species in the removal of diesel from DCS. This could be explained mainly by the oxidative degradation and the consequent volatilization. When assessing biocompatibility based on phytotoxicity and microbial toxicity, it was possible to conclude that effectiveness of this approach for the use in the environment. Plasma-generated reactive species' phenomena such as physical and chemical effects on the soil, plant development, and microbial activity in the soil and human skin cells were also discussed in the study. Thus, this work also points to the possibility of MEDBD plasma in mitigating DCS and prospects to be explored in the next real field/large scale experiments.

In the second study, this thesis assessed how argon (Ar) and argon mixed with air (Ar-Air) plasma jets performed in breaking down 4-nitrophenol (4-NP) that showed promising results in reducing pollutant levels and toxicity. Through the integration of atmospheric air into the plasma discharge zone the Ar-Air plasma jet notably enhances the formation of reactive oxygen and nitrogen species (RONS). This modification proves effective in addressing 4-NP pollution in deionized water (DW). The Ar-Air plasma jet surpasses the Ar jet, achieving a higher degradation rate of 97.2% and maximum energy efficiency of 57.3 gkW⁻¹h⁻¹ over a 6 min treatment with 100 mgL⁻¹ 4-NP in DW. Furthermore, the Ar-Air plasma jet exhibits a notably higher first-order rate coefficient for 4-NP degradation. This thesis concluded that the degradation of 4-NP is attributed to electron transfers produced by plasma, energy derived from excited species, and the combined effects of reactive oxygen species (ROS). Additionally, this thesis assessed the biotoxicity and phytotoxicity of the processed 4-NP to guarantee its biological safety.

In the third study, this thesis has investigated the environmental impact of plasma remediation for synthetic textile dyes contaminated water. Using the MEDBD plasma, this thesis has selectively produced O₃ and NO for degradation of various synthetic textile dyes for effective dye degradation. The obtained results indicated the MEDBD system's potential as a sustainable solution for treating dye-contaminated water in industrial settings. Notably, the O₃ generator plasma achieved over 96% degradation of dyes like methylene blue (MB), Congo red (CR), methyl orange (MO), crystal violet (CV), and Evans blue (EB) with just 2.4 W of plasma power. From the various analysis, this thesis has confirmed that the proposed mechanism for dye degradation involved plasma-generated aqua electrons, excited species, and ROS (O₃, H₂O₂, and OH·), leading to dye oxidation into simpler forms like CO₂, H₂O, and N₂. To sum up, the MEDBD plasma generated with O₃ dominated source could effectively be used for degradation of various synthetic dyes from dye contaminated water in lab to industrial scale.

The fourth study analyzed the optical, structural, and morphological properties of the green synthesized chitosan-functionalized gold nanoparticles (Au@CS NPs) using a NTP jet. This study opened the new avenues for gold nanoparticles (Au NPs) synthesis with the functionalization of chitosan (CS) using efficient and straight forward method. The study introduced a green single-step synthesis method using the NTP jet to produce uniform Au@CS NPs that utilized plasma generated electrons, hydrogen atoms, and RONS for reduction of gold ions and oxidation of CS in acidic environment simultaneously. Importantly the use of a 3% hydrogen mixed Argon gas as an optimized feeding gas for NTP jet enhances the efficiency of Au@CS NPs synthesis. To conclude, this pioneering research underscores the environmentally friendly nature of plasma-liquid interaction for Au@CS NPs synthesis, which can be further used for various applications ranging from biomedical to optical sensing applications and many more.

In the fifth study, this thesis synthesized citrate-stabilized silver nanoparticles (Ag@Cit NPs) using a plasma-assisted reduction method that offered insights into the relationship between plasma parameters and NPs characteristics. Here this thesis examines the synthesis, characteristics, and catalytic applications of plasma-synthesized Ag@Cit NPs using varying plasma plume length. This plasma synthesized Ag@Cit NPs utilizing different plasma plume lengths revealed their catalytic properties for dye degradation in dye contaminated wastewater treatment. Here this thesis mainly focused on the influence of plasma plume length on structural, optical, and dye degradation properties. The Ag@Cit NPs exhibited a quasi-spherical shape with an average diameter of 5.9-7.5 nm, showing absorption peaks at around 406 nm. Their quantity increased with plasma exposure duration, particularly in the 8.5 cm plume of jet, indicating a synergetic effect between plasma electrons and citrate. In summary, plasma-assisted citrate reduction facilitated synthesis, and their citrate-capped nature ensured stabilization in Ag@Cit NPs for the significant methylene blue dye degradation by plasma-synthesized Ag@Cit NPs as a catalyst.