Urbanization and increased industries contribute to environmental degradation, exposing the environment to hazardous contaminants and microbes. Sustainable living conditions for future generations require thorough research on environmental remediation, which involves reducing or eliminating contaminants from air, water, and soil [1]. Wastewater treatment plants restore contaminated water to usable state, addressing chemical, physical, physiological, and biological environmental pollutants, including inorganic and organic pollutants containing organic carbon [2]. Organic pollutants, including oil and synthetic compounds, require oxygen to break down, causing aquatic life to suffer. Dyes are another type of organic pollutants that cause significant environmental pollution [3].
Water quality issues have arisen due to the bacterial and complicated structural material contamination of water streams [4]. Due of the complexity of their organic makeup and difficulty in decomposing, these dyes are difficult to remove from water using current treatment techniques. Numerous techniques, such as coagulation, adsorption, biological degradation, etc., have been employed [5]. At present, dyes, pigments, and color products are essential to many processes, including food manufacturing, cosmetics, medicines, leather goods, beverages, and paper industries [6]. It has a complicated structure, not biodegradable, and is detrimental to plants, animals, and the environment. The global dye market produces around 700,000 different dye types each year, the majority of which are released into the environment from the textile industry and damage water supplies [7]. The textile industry’s growing demand for dyes has led to wastewater containing with dye, which is only partially treated and eventually discharged into the sewage system, posing a serious environmental problem due to its potential to pollute lakes, rivers, and streams [8].
Conventional dye removal techniques consist of physical, chemical, and biological methods. Physical methods like ion exchange, adsorption, and membrane filtration are used to recover valuable materials and separate large dissolved matter. Adsorption is more efficient but inefficient due to its limited reuse [9, 10]. Chemical dye removal methods are divided into two categories: traditional chemical treatments and chemical oxidation techniques [11]. Traditional chemical treatment methods such as adsorption, coagulation, and electrochemical shift pollutants, resulting in secondary pollution [12]. Oxidation is effective for large-scale wastewater treatment but insufficient for contaminated wastewater, emphasizing the importance of effective pollutant removal. Biological treatment has been used to treat wastewater for more than 150 years [13]. The biological technique is preferred over physical and chemical methods because it produces no hazardous byproducts and is less expensive on an industrial scale [14]. NP synthesis using biomass is a green chemistry method that uses less energy and is free from toxic substances. It allows for the development of preventive, safer chemical synthesis, renewable feedstock, and reductive derivatives [15].
Plant extract is widely used as a key component in the synthesis of nanoparticles due to its safety and viability. Plant derived proteins, carbohydrates, enzymes, phenolic acids, and alkaloids are utilized in the reduction and stabilization procedures. When plants are used as biological substrates, there is less need for chemicals to act as reducing, capping, and stabilizing agents for the formation of metal nanoparticles from their respective precursor solutions because they contain many key phytochemicals [16]. A safe, biocompatible, and ecologically friendly approach is often used in green synthesis since leaves have a lot of metabolites [17].
In dyeing, printing, cosmetics, and leather industries, MB is the most extensively used cationic dye [18]. MB is a heterocyclic aromatic basic dye [19]. MB, a well-known cationic and primary thiazine dye, has the chemical formula C16H18ClN3S and a maximum absorption wavelength of 664 nm. At room temperature, MB is a solid, odorless dark green powder that dissolves in water to form a blue solution [20]. Due to its high toxicity, MB dye is hazardous to human health above a specific quantity [21]. MB is toxic, cancer-causing, and not biodegradable. Releases of MB dyes into aquatic steams prevent sunlight from penetrating, which kills aquatic species. It increases the risk of several illnesses, such as vomiting, diarrhea, respiratory problems, and skin irritation. The current challenge is to degrade and eliminate these dyes before they are discharged into water bodies [22]. Solar energy is the most efficient and straightforward method for removing colors from dye effluent and it is readily available, produces no sludge during degradation, and is relatively inexpensive when compared to other methods [23]. For the degradation of MB dye, ZnO Nps is utilized in photocatalytic degradation (UV/Solar irradiation). ZnO nanoparticles (ZnO NPs) have a variety of possible uses, including those in cosmetics, textiles, microelectronics, catalysts, semiconductors, antimicrobials, photocatalysis, and environmental cleanup [24]. Metal oxides have high surface area, low production, and regeneration costs, making them effective in degrading organic contaminants [25]. Activated carbon, produced from carbon rich natural resources, is commonly used for wastewater treatment. However, some commercial activated carbon is expensive. Low cost agricultural byproducts are being explored as alternatives, offering practical solutions for wastewater treatment and waste reduction [26, 27].
In the current work, ZnO Nps and AC@ZnO were prepared using leaves of Averrhoa arambola L in accordance with the green synthesis method in order to test their ability to degrade MB in water. Both sample characterization and photocatalytic degradation parameter optimisation were looked at. The resulting materials may exhibit high surface areas and larger pore volumes. The impact of ZnO and the ratio of AC to ZnO impregnation on structural characteristics was examined. Additionally, the ability of the ZnO Nps and AC@ZnO to absorb MB from aqueous solutions was evaluated at different starting concentrations, carbon doses, pH levels, and temperatures. To ascertain the mechanism underlying adsorption and forecast the rate of adsorption, the adsorption isotherms and kinetic was also investigated.