Removal of industrial dye and pharmaceutical contaminants using platinum nanoparticle-decorated rough particles: A comparative study of interfacial and bulk decontamination approaches

Abstract

Active pharmaceutical ingredient (API) and formulation industries pose significant risks to aquatic ecosystems and human health upon entering lakes and rivers. These contaminants arise from various phases of pharmaceutical production, including manufacturing, formulation, and disposal processes, as well as residues found in agricultural and hospital wastewater. Because of their biological effects and broad consequences on surroundings, even at low concentrations, the pollutants from APIs are starting to cause some adverse effects. When these drugs find their way into water systems via poor disposal techniques or industrial effluents, they linger and build up to have negative consequences. Subsequently, these residues can affect aquatic life’s reproductive systems, challenging environmental sustainability and public health. Advanced wastewater treatment technologies can efficiently eliminate trace pollutants and help to reduce potential hazards. Sonochemical procedures, microwave treatment, and ozonation methods can reduce the environmental impact of pharmaceutical residues. Still, scalability and operation costs are of concern for most of these methods. Similarly, the textile sector significantly adds to water pollution by discharging wastewater containing dangerous chemicals from production operations. Different modern treatment technologies are used to mitigate the pollutants of this kind from wastewater. The ozone-based treatment removes various organic and inorganic contaminants, including drugs and colours. On the other hand, microwave radiation can accelerate chemical reactions and eliminate organic compounds by breaking them down into less harmful products. When using conventional techniques such as ultrasonic waves, the sonochemical treatment generates radicals that break down pollutants like industrial chemicals and drugs, minimizing their concentration in wastewater. Similarly, the sono-Fenton process generates hydroxyl radicals, known for their effectiveness in oxidizing and breaking down organic contaminants. Every treatment approach has advantages and can be adjusted to target particular pollutants. However, these techniques have certain disadvantages when treating large volumes of wastewater. They include 1) high running expenses and 2) restricted scalability. Many of these techniques also generate secondary wastes called sludge that require additional treatment and disposal, complicating and making the entire process expensive. Furthermore, less appealing elements are high energy requirements in sonochemical treatment, severe pH requirements in Fenton-based processes, and large hydrogen peroxide consumption in Fenton and photo-Fenton techniques. Chapter 3 illustrates a simple yet straightforward methodology for fabricating rough particles at room temperature in a single step. These particles exhibit high catalytic efficiency (100% removal) against methylene blue and tetracycline within a reasonable time frame. Characterization techniques such as X-ray diffraction (XRD), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM) confirm the uniform deposition of platinum nanoparticles on polystyrene surfaces, forming dense islands and a roughened texture. Particle size, concentration, and contact patterns significantly influence catalytic performance, with semi-batch conditions favouring tetracycline decomposition in 40 minutes and batch-wise operation achieving maximal methylene blue degradation within 10 minutes. The heterogeneous catalytic process follows pseudo-first-order kinetics modelled by Langmuir-Hinshelwood kinetics, with rate constants of 0.048 and 0.032 min−1 for 0.6 and 1.0 μm particles, respectively. Magnetically responsive nanoparticles demonstrate potential for real-time applications, enabling efficient catalyst recovery via external magnetic fields without additional costs. Chapter 4 demonstrates the removal of methylene blue using rough particles decorated with Pt nanoparticles at the air-water interface. It can be shown later that the catalytic removal rate can be efficiently controlled by a few other factors apart from the dosing, the volume of hydrogen peroxide, and the sizes of the particles used. The degradation of pollutants at the air-water interface is emphasized instead of through a bulk process. One potential advantage of an interfacial approach could be the simultaneous removal of oil-soluble and water-soluble impurities from the bulk phases. This study uses a reactor to leverage rough particles at the air-water interface combined with a controlled circulation system, enhancing mass transfer and reaction kinetics to remove target contaminants. Further, this chapter demonstrates that the packing factor and circulation speed can alter the decomposition kinetics to warrant optimized performance. The importance of these parameters is highlighted, showing that rapid removal of methylene blue occurs within 30 minutes at a circulation speed of 50 rpm and a particle packing factor of 0.8. This programmed speed indicates rapid catalytic activity at the particle interface. Moreover, the interfacial approach shows that the effectiveness of methylene blue removal is slightly better than that of the bulk system. At the interface, the catalytic surface area for reactions involving hydrogen peroxide is made more readily available, enhancing the rapid catalytic activity of the particles. This strategy promotes the swift degradation of the target pollutant, methylene blue. Chapter 5 demonstrates recent advancements in fuel-responsive micromotors and highlights their promising applications for environmental cleanup, though issues such as reaction losses from particle aggregation have become apparent. In this research, two types of particles have been investigated: passive particles with a full platinum nanoparticle coating and active particles with platinum partially coated on their surfaces. This study used various techniques-energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS)-to verify the selective application of platinum on the hematite cores. These techniques offered a detailed view of the surface characteristics of the micromotors enhanced with Pt nanoparticles. When platinum nanoparticles on one side of the hematite particles decompose hydrogen peroxide (H2O2), they generate thrust that propels the particles in a specific direction. This directed propulsion enhances the micromotors’ effectiveness in interacting with pollutants and navigating their environment. Microscopy images revealed that agglomeration occurs during the Fenton-like reaction for both particle types. Passive particles showed significant clustering over time due to magnetic dipolar forces. This study on Janus active particles (micromotors) shows that self-propulsion powered by H2O2 can minimize these magnetic interactions, lowering the formation of irregular clusters and raising the overall micromotor efficiency.