INTRODUCTION

Background on Organic Pollutants

Organic pollutants are versatile as far as their carbon-containing structures and spanning forms are concerned, and as such, they can remain in the ecosystem for long periods of time. These include synthetic dyes from textile industries, pharmaceuticals from household and hospital waste, and pesticides used in farming. The profound benefits these compounds have provided in terms of living standards and agricultural output is in serious jeopardy due to their bio accumulating properties.

Sharp and Azo Dyes used in various textile and paper industries stand out as some of the most dangerous and tenaciously persistent chemical pollutants. Aquatic vegetation can suffer from the inhibition of photosynthetic activity due to silencing of decomposition light, pH alterations, and toxic metabolite generation during cleaving even at very low concentrations of dyes (Ahmad et al., 2024). It is the aromatic constituents of such compounds that are resistant to microbial degradation which allows them to stay in dye-infested water bodies for prolonged periods.

A range of waterborne substances such as antibiotics, hormones, and pain-relievers are wasted, biologically excreted, or carelessly dumped by industries. The very existence of these compounds result in issues due to their endocrine disrupting action and aggravate the prevalence of superseded organisms. Even the slow and steady increment of these compounds, regardless of the quantity, can interfere with the reproductive capabilities of marine organisms and bio magnify through the food chain.

Organophosphate and carbonated pesticides that are heavily utilized in agriculture practices contaminate water, soil, and air (Haruna et al., 2024). Persistent organic pesticides (or DDT and aldrin) are, infamously, known for their cancer causing abilities and long half-life. In addition to the issues that they bring to target pests, these substances also negatively impact disease processes in humans and biomedicine, pose a challenge in terms of international agricultural safety, and biodiversity. 

Depreciation of Classic Techniques of Disposal 

Tackling organic pollutants includes a wide variety of methods like physical, chemical, and biological approaches. Such methods, however, have their respective damaging shortcomings in regards to eco-friendliness and efficiency. While effective in the removal of pollutants, sedimentation and carbon adsorption, micro screening, filtration, as well as membrane processes do not completely destroy them (Deng et al., 2021). Treatment processes, which can contribute to new pollution, only change the form of the pollutants and require additional forms of treatment. 

Destructive processes such as chlorination, zonation and even AOPs (Advanced Oxidation Procedures) fall under the category of aggressive interferent reliant and energy demanding treatments. For example, waste chlorination is known to create gas generating trihalomethanes which are classified as carcinogenic compounds. In addition to that, their non-selective nature within intricate waste mixtures renders them less useful.

Activated sludge process treatment and anaerobic digestion are relatively efficient and green biological treatments methods, but they are also slow and sensitive to temperature. Due to their intricate molecular structures, many organic compounds are only partially biodegradable. Some antibiotics and pesticides, for example, can inhibit microbial action or resist enzymatic disintegration (Boulkhessaim et al., 2022). Apart from that, more traditional methods are often difficult to scale, too expensive, or fail to integrate contemporary rigorous stratified environmental governance systems. These challenges need new designs that are socially and ecologically innovative. 

Eco-friendly and sustainability focused approaches have emerged as primary drivers of innovation. That said, there is growing demand for sophisticated and low-cost designs aimed at minimizing environmental damage. This change towards green approaches is aided by multiple factors: Environmental responsibility: Conventional technologies result in further pollution and climate change through the uncontrolled release of energy and harmful wastes. Greener technologies should aim to ensure that all processes undertaken have products that are ecologically safe and non-harmful. 

●       Sustainability: The EU Water Framework Directive and Clean Water Act set a limit for pollutants which improves a country’s environmental rating and requires eco-friendly means for pollution reduction.

●       Public health concerns: Clean sources of water are essential due to emergent water borne diseases, the use of antibiotics, and the exposure to chemicals causing hormonal disruption.

●       Resource efficiency: Green technologies help in the prevention of waste creation, damage to renewables, and the maximization of the atom economy which means the useful conversion of reactants to products of interest.

Hence, the demand in the innovation for wastewater treatment technologies has changed to green catalysis, where degradation mediated by catalysts is done in an environmentally safe manner.

Introduction to Green Catalysts

Their Role Green catalysts are materials that assist in performing a chemical reaction without being fully consumed in the process under mild conditions. These catalysts represent the advancement in the efforts of green chemistry to reduce the generation of waste, the negative impacts of substances and energy consumed (Taoufik et al., 2022). These include natural enzymes, bio char supported catalysis, metal-free catalysts, and plant extracts.

Types of Green Catalysts Photocatalysts, such as TiO₂ and ZnO with Addition of Green agents, are catalysts that utilize sunlight or visible light, producing oxygen species that break down complex organic molecules.

●       Biocatalysts: These include bionic enzymes laccase and peroxidase laccase and peroxidase laccase and peroxidase, respectively extracted from fungus and bacteria. They act in the destruction of phenolic compounds, dyes, and even pharmaceuticals at moderate temperatures.

●       Nano catalysts: These biosynthesized nanoparticles, for example Eg and Fe₃O₄, have both a high surface area and reactivity and are synthesized from plant extracts. They removed pollutants through redox reactions or Fenton-type processes.

●       Carbon-based catalysts: These include doped graphene and transformed activated biochar, which are produced from waste biomass. They serve as scaffolds for catalytic sites and as active participants in electron transfer reactions.

Green catalysts serve the purpose of improving:

●       Effectivity along with selectivity in pollutant degradation. 

●       Minimal costs and sustained usability. 

●       Reduced energy expenditure, as the catalyst needs little activation energy in normal conditions or sunlight. 

●       Virtually no secondary pollutants and negligible biocatalysts’ biodegradability.

Aim/ Question and Objectives of the Study

Aim

For that, we develop and evaluate eco friendly green catalysts for the effective degradation of organic pollutant in the wastewater based on the parameter of catalytic performance, environmental impact and scalability.

Research Question

What are the degradations of organic contaminants using green catalysts such as biosynthesized nanoparticles, enzyme based systems and biochar supported material under environmentally relevant condition and how do they compare to standard methods of treatment in terms of efficiency, reusability, and sustainability?

Objectives

●       Identify and develop eco-friendly catalysts with high activity toward organic pollutants like pesticides, pharmaceuticals, and dyes.

●       To assess how different levels of pH, temperature, and concentration of pollutants changes the catalytic activity within materials, relevant degradation processes will be optimized. 

●       To confirm that the resultant byproducts from the decomposition of contaminants are non-toxic, processes are analyzed with advanced techniques including UV-Vis spectrophotometry, FTIR, GC-MS and others.

●       The time of reuse and the stability of the green catalysts over multiple cycles will be evaluated in order to determine their practical application value.

●       The green catalytic degradation process will be analyzed in comparison to other treatment methods regarding efficacy, cost, energy consumption, and environmental impact.

This study will attempt to solve water pollution issues by using eco-friendly methods that fulfill the objectives of the UN Sustainable Development Goals, specifically SDG 6 (Clean Water and Sanitation) and SDG 12 (Responsible Consumption and Production).

Humans and the environment are greatly threatened by organic pollutants due to the treatment methods devised for them which are not sophisticated enough to fully eradicate and neutralize their existence, as well as their toxic effects. The use of green catalysts is a sustainable solution to this problem as they present a high level of degradation efficiency and a low ecological risk. This study plans to apply the principles of green chemistry to step-by-step the designing of scalable water treatment technologies that would reduce the costs for deploying remediation systems aimed at environmental restoration.

LITERATURE REVIEW

Types of Organic Pollutants Overview and Their Effects on the Environment 


Figure 1: Organic Pollutants

These compounds are often composed of carbon structures that are persistent in nature. Some examples are synthetic dyes, pharmaceuticals, pesticides, petrochemicals, phenolic compounds, and phthalates and bisphenol A, which are classified as plasticizers. Each type has a different origin and poses a distinct threat to nature. For instance, synthetic dyes used for marking and coloring in the textile and printing industry are non-biodegradable and pose a danger to aquatic life because of their vibrant colors and intricate structures (de Farias et al., 2022). Pharmaceuticals such as antibiotics, hormones, and anti-inflammatory medicines are often discarded and excreted, along with wastewater from hospitals and drug manufacturing plants. Their presence, even in traces, is known to promote antimicrobial resistance and disrupt endocrine functions in living organisms. Pesticides, most importantly persistent organic pollutants like DDT and organophosphate pesticides, are widely utilized in agriculture. Their tendency to bio accumulate in non-target organisms, such as birds and humans, renders them extremely toxic. These pollutants cannot be removed by conventional techniques of treating wastewater and, thus, contaminate water and soil, which further results in the imbalance of health problems, deterioration of the ecosystem, and degradation of the environment for a long period of time. The difficult behaviors and destructive features of these substances demonstrate the need for a more effective and ecologically considerate treatment method.

Computational Chemistry: A Sustainable Tool in Green Catalysis


Communication chemistry represents a theoretical chemistry field which combines computerized simulations with chemical theory for solving chemical problems. This method has brought a fundamental change to the way researchers study and develop eco-friendly catalysts through green catalysis research. Computational chemistry serves as an efficient tool which replaces traditional experimentation because it needs fewer resources along with shorter duration and reduced materials usage. The technique enables scientists to analyze complex reactions and study molecular structures together with the evaluation of reactivity and prediction of outcomes in diverse environmental conditions using computer simulation prior to conducting physical experiments.

The development of efficient selective reusable environmentally friendly catalysts for green catalysis depends highly on computational chemistry applications. Through quantum mechanical calculations researchers along with molecular modeling enable identification of catalyst electronic structures and active sites while determining reaction mechanisms at the atomic level. The obtained scientific knowledge helps researchers create better performing catalysts which produce minimal environmental impact and reduce resource usage.

The predictive computational method used most frequently in catalyst research is Density Functional Theory (DFT). Through DFT calculations scientists gain the ability to study reaction energy profiles as well as interpret activation barriers and measure intermediates' stability. The modeling of pollutant molecule interactions with catalyst surfaces like Fe₃O₄ or TiO₂ doped with plant-based agents happens through density functional theory when evaluating degradation processes of dyes or pharmaceutical residues. This analytical method exposes which orientations the adsorbates prefer while displaying transfer mechanisms and breaking mechanisms which serve to enhance catalyst effectiveness.

MD simulations serve as a crucial application to study the time-dependent atomic and molecular behavior through their time-evolving dynamics. Aqueous catalytic systems depend on MD to better understand the effects of solvent molecules as well as the movement of reactants and catalysts and their temperature-dependent properties. Enzyme-based green catalysts require special attention because their performance directly correlates with pH and temperature sensitivity in their environment. MD simulations show the structural changes of enzymes and their consequent effects on pollutant breakdown performance.

The process of catalyst green synthesis evaluation heavily depends on computational methods for route screening. A computational approach predicts which phytochemicals including flavonoids, terpenoids and polyphenols have the capability to stabilize nanoparticles while boosting redox potential rather than conducting experimental tests for hundreds of bio-sources in nanoparticle synthesis. The predictive model follows green chemistry principles through its reduced need for experimental errors along with waste reduction and resource maximization strategies.

While computational chemistry serves as a tool for conducting toxicity analysis and safety evaluations regarding environmental sustainability. In silico toxicity prediction tools help identify possible environmental hazards that develop from degradation intermediates and reaction products. QSAR (Quantitative Structure-Activity Relationship) modeling tools determine biological and ecological effects on chemical products so green catalysis removes main pollutants while preventing dangerous secondary product formations.

QM/MM (Quantum Mechanics/Molecular Mechanics) serves together with hybrid computational methods to obtain valuable information on enzyme catalysis processes. Quantum mechanical analysis of enzyme active sites pairs its accuracy with molecular mechanical analysis of remaining structural regions to yield extensive understanding about biological catalytic processes in real environments.

Computational chemistry appeals to scientists because it delivers high value for money. Real-world simulations of high impact become accessible to all research institutions due to steadily increasing accessibility of high-performance computing technologies alongside open-source software availability. The DFT and electronic structure analysis utilizes software packages such as Gaussian, ORCA and VASP and Quantum ESPRESSO but GROMACS and LAMMPS serve as platforms for MD simulations.

Green catalysis receives improvements through computational chemistry by facilitating the development of environmentally friendly catalytic systems and their mechanism-oriented analysis and precise data predictions. This approach makes sustainability possible because it minimizes experimental costs and supports economical synthesis while providing early toxicity assessment during safety analysis. The growth of computational power establishes an essential position for it in green chemistry and environmental remediation.

The Birth of Catalytic Degradation (Heterogeneous and Homogeneous Catalysis)

The effort to purify water through catalytic oxidation methods in the early 1900s marked the start of discovering catalysts for the degradation of pollutants. Since then, two types of catalytic systems have emerged: homogeneous and heterogeneous catalysis. Homogeneous catalysts that are usually in the same phase as the reactants are most commonly some sort of a soluble metal complex or an acid. Effervescent catalysts tend to operate at higher rates and greater selectivity, but pose difficulties with removal as they become entwined with secondary pollution risks (Bala et al., 2022). On the other hand, heterogeneous catalysts that exist in a different phase are usually solid catalysts in a liquid or gaseous reaction mixture. Heterogeneous catalysis is more widely used with systems that require ease of separation and reusability, as well as being more favorable for continuous processes. Early examples include the use of transition metal oxides like TiO2 and MnO2 in oxidative degradation processes. Catalytic systems have gradually become more sophisticated, incorporating designs such as Fenton and photo-Fenton reactions where iron catalysts produce hydroxyl radicals which serve to further oxidize pollutants.

 

Figure 2: Catalysts

Since then, catalysis has been at the core of advanced oxidation processes (AOPs), but the fixed catalysts used are always poisonous and depend on large amounts of metals, high energy, and harmful chemicals that damage the environment.

In this sense, the focus on non-renewable and potentially dangerous catalytic materials available has changed in the past few decades towards more sustainable and environmentally friendly options.

Principles of Green Chemistry relative to Degradation of Pollutants