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Review Article
ARTICLE IN PRESS
doi:
10.25259/JQUS_39_2025

Green Synthesis of Metal Oxide Nanoparticles Using Plant Extracts for Removal of Berberine Hydrochloride from Wastewater: A Comprehensive Review

, , ,
1Department of Chemistry, College of Science, Qassim University, Buraydah, Qassim, Saudi Arabia
2Department of Chemistry, Department of Chemistry, College of Science, King Saud University, Riyadh, Saudi Arabia.

* Corresponding author: Prof. Sayed M. Saleh, Ph. D, Analytical Chemistry, Department of Chemistry, College of Science, Qassim University, Buraydah, 51452, Saudi Arabia. e.saleh@qu.edu.sa

Received: , Accepted: ,
© 2026 Journal of Qassim University for Science - Published by Scientific Scholar
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This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

How to cite this article: Almalki AJ, Alterary SS, El-Tohamy MF, Saleh SM. Green Synthesis Of Metal Oxide Nanoparticles Using Plant Extracts For Removal Of Berberine Hydrochloride From Wastewater: A Comprehensive Review. J Qassim Univ Sci. doi: 10.25259/JQUS_39_2025.

Abstract

Water pollution caused by pharmaceutical residues, particularly berberine hydrochloride (BRB), has emerged as a significant environmental challenge in recent decades. Conventional wastewater treatment plants are not specifically designed to remove complex organic micropollutants, such as pharmaceuticals, so these compounds persist in aquatic ecosystems and can cause ecotoxicological effects. Advanced oxidation processes and photocatalytic degradation using metal oxide nanoparticles (NPs) have shown remarkable promise for addressing this pollution. Among these, titanium dioxide (TiO₂) NPs synthesized via green chemistry approaches using plant extracts represent a sustainable, environmentally friendly solution. This comprehensive review examines the properties, synthesis methods, and photocatalytic mechanisms of TiO₂ NPs for BRB degradation. We discuss the factors influencing catalytic efficiency, including surface area, crystalline structure, particle size, and operating conditions such as pH, temperature, and light irradiation. Furthermore, this review highlights the potential of plant-mediated synthesis using local flora such as Scirpoides holoschoenus, a sedge native to Saudi Arabia, as an innovative and sustainable approach to nanomaterial fabrication. The integration of green chemistry principles with nanotechnology offers promising opportunities to develop cost-effective, non-toxic, and environmentally sustainable solutions for removing pharmaceutical pollutants in wastewater treatment systems.

Keywords

Berberine hydrochloride
Green synthesis
Photocatalysis
Plant-mediated synthesis
Scirpoides holoschoenus
Titanium dioxide nanoparticles
Wastewater treatment

INTRODUCTION

Overview of water pollution

Water pollution caused by pharmaceutical residues has become a major environmental problem in recent decades. As global consumption of pharmaceuticals increases due to population growth, aging populations, and improved access to healthcare, the occurrence of these compounds in aquatic ecosystems is also growing.[1] Among the most persistent and worrisome are pharmaceutical compounds that enter the environment through various pathways, such as human and animal excretion, improper disposal of unused drugs, and wastewater from pharmaceutical manufacturing facilities and hospitals.[2]

While conventional wastewater treatment plants remove many common pollutants, such as suspended solids, organics, and nutrients, they are not explicitly designed to remove complex organic micropollutants, such as pharmaceuticals.[3] As a result, these substances can pass through the treatment processes and enter the receiving waters. Other sources of pharmaceutical pollution include the improper disposal of unused medicines, runoff from agricultural land treated with pharmaceutically contaminated manure or veterinary drugs, and wastewater from hospitals and pharmaceutical manufacturing facilities.[4] The ecological consequences of pharmaceutical contamination are considerable and diverse. Continuous exposure to low concentrations of bioactive compounds can alter the behavior, reproduction, and survival of aquatic organisms. For example, studies have shown that certain hormones and endocrine-disrupting compounds can feminize male fish. At the same time, environmental antibiotics contribute to the spread of antibiotic-resistant bacteria, posing a serious threat to public health. In addition, the long-term and cumulative effects of complex pharmaceutical mixtures in the environment remain poorly understood and are the subject of ongoing scientific research.[5]

Another challenge is the chemical diversity and the varying physicochemical properties of pharmaceutical compounds, which make them difficult to remove from wastewater. Some are highly soluble in water; others are hydrophobic and tend to adsorb to organic matter or sediments; and many are resistant to degradation. Their transformation products, which may result from partial degradation or treatment, can be as toxic or even more toxic than the parent compounds.[6] These pharmaceutical pollutants are often not completely removed by conventional wastewater treatment processes, as these processes usually do not target complex organic compounds such as antibiotics, hormones, analgesics, and alkaloids, such as berberine hydrochloride (BRB). As a result, traces of these substances remain in the treated water and can accumulate in natural waters. Over time, this contamination can disrupt aquatic ecosystems, contribute to the development of antibiotic-resistant bacteria, and pose risks to human health through the water supply chain.[7] BRB, a plant-based isoquinoline alkaloid with antimicrobial and anti-inflammatory properties, has attracted attention as a model pollutant for pharmaceuticals due to its widespread use and stability in aquatic environments. Its persistence and potential ecotoxicity make it an ideal candidate for studies focusing on advanced water treatment technologies.[8]

In response to this growing challenge, researchers have turned to nanotechnology solutions, particularly metal oxide nanoparticles (NPs), as promising candidates for degrading pharmaceutical impurities.[9] These materials offer a large surface area, unique catalytic properties, and tuneable physicochemical characteristics, thereby increasing their efficiency in degrading complex organic molecules. The development of environmentally friendly metal oxide NPs is a sustainable and practical approach to combat pharmaceutical pollution and advance wastewater treatment.[10]

Berberine hydrochloride

In recent years, the presence of pharmaceutical compounds in aquatic environments has gained significant attention from researchers, environmental regulators, and public health authorities.[11] Among these compounds, BRB, a plant-derived isoquinoline alkaloid, has emerged as a notable contaminant due to its widespread use and persistence in wastewater systems. Although traditionally used in herbal medicine, BRB is now widely available in pharmaceutical formulations and dietary supplements, thereby increasing its environmental footprint. This compound, once thought to be environmentally benign due to its natural origin, is now recognized for its potential ecotoxicological effects and resistance to degradation, making it a model compound for studying pharmaceutical pollution in water bodies.[12]

Chemical nature and sources of BRB

Berberine is an alkaloid found in a variety of medicinal plants, including Berberis vulgaris (barberry), Coptis chinensis (Chinese goldthread), and Hydrastis canadensis (goldenseal). Berberine is commonly used as BRB, a salt that improves its solubility and bioavailability. Chemically, BRB is a quaternary ammonium salt with the molecular formula C20H18ClNO4 [Figure 1]. It is known for a wide range of pharmacological activities, including antimicrobial, anti-inflammatory, antidiabetic, hypolipidemic, and anticancer properties. These therapeutic effects have led to its inclusion in over-the-counter medications and nutraceuticals for the treatment of gastrointestinal infections, metabolic disorders, and cardiovascular diseases.[13]

Chemical structure of BRB.
Figure 1:
Chemical structure of BRB.

Due to its increasing medical and commercial applications, BRB enters aquatic environments through various pathways:

Human excretion: Like many other pharmaceuticals, the human body partially metabolizes BRB, and a significant fraction is excreted unchanged or as active metabolites via urine and feces. These residues ultimately reach municipal wastewater treatment systems.[14]

Industrial effluents: Pharmaceutical manufacturing plants and herbal medicine processing units may discharge BRB directly into wastewater streams if not properly regulated.[15]

Hospital and healthcare waste: Improper disposal of medical waste, including used or expired drugs containing BRB, can lead to localized contamination.[16]

Agricultural runoff: In some traditional or veterinary practices, animal caregivers use herbal preparations containing berberine, and residues enter the environment through manure and irrigation runoff.[17]

Persistence and behavior in aquatic environments

One of the key environmental concerns associated with BRB is its chemical stability and resistance to degradation in conventional wastewater treatment plants. BRB is a highly conjugated aromatic compound with strong resistance to photolysis and microbial degradation under standard treatment conditions. Its quaternary ammonium structure and water solubility further enhance its mobility in aquatic systems, allowing it to persist in surface waters, groundwater, and even drinking water sources at trace levels.[18] Studies have shown that BRB can adsorb onto sediments and suspended solids, but a significant fraction remains in the aqueous phase. Its high bioactivity at low concentrations means that even minimal environmental presence can cause biological effects in non-target organisms. Moreover, under certain conditions, BRB can undergo partial degradation, leading to the formation of intermediate by-products, some of which may be more toxic or persistent than the parent compound.[19]

Ecotoxicological and environmental impact

Although BRB is of natural origin, its bioactive nature poses risks when introduced into non-target environments. Its antimicrobial properties, while beneficial in medicine, can disrupt microbial communities in aquatic ecosystems when it is released into wastewater. These microbial populations are essential for maintaining ecological balance, nutrient cycling, and self-purification in natural water bodies.[20]

Key concerns about BRB as an environmental pollutant

Disruption of microbial ecology: BRB can inhibit the growth of beneficial bacteria in aquatic systems, leading to imbalances in microbial populations that are vital for ecosystem health.[21]

Antibiotic resistance: Prolonged exposure to sublethal concentrations of BRB and other antimicrobial agents can contribute to the emergence and spread of antibiotic-resistant genes in environmental bacteria, posing a long-term threat to human and animal health.[22]

Toxicity to aquatic organisms: Experimental studies suggest that BRB may be toxic to algae, daphnia, and fish, particularly under chronic exposure. It can affect growth, reproduction, enzyme activity, and oxidative stress responses, even at low concentrations.[23]

Endocrine disruption: Although research remains limited, some findings indicate that BRB may have endocrine-disrupting potential, particularly when it interacts with other pharmaceuticals and environmental pollutants.[24]

Monitoring challenges and regulatory gaps

Most national and international water quality standards do not currently list BRB as a priority pollutant. As a result, there are limited monitoring programs and risk assessment frameworks specifically targeting this compound. However, its increasing detection in water samples has prompted calls to include it on broader lists of emerging contaminants.[25] A significant challenge in addressing BRB pollution is the limited removal efficiency of conventional wastewater treatment technologies. Standard biological processes, such as activated sludge systems, do not fully degrade BRB, leading to its release into natural water bodies, which has created a demand for the development and implementation of advanced treatment methods, including photocatalysis, advanced oxidation processes, adsorption with nanomaterials, and membrane technologies.

LITERATURE REVIEW

Methods for removing BRB from wastewater

Advanced oxidation processes (AOPs): O₃/UV/H₂O₂

A combination of ozone (O₃), ultraviolet (UV) light, and hydrogen peroxide (H₂O₂) is highly efficient in degrading BRB. Under optimized conditions (initial pH 7.0, H₂O₂ dosage of 3 mM, O₃ dosage of 10.3 mg min-1, and 45 min reaction time), the process achieved up to 94.1% removal of BRB (initial concentration 1500 mg L-1). Additionally, treated wastewater showed a significant improvement in biodegradability, as reflected by a 15-fold increase in the BOD₅/COD ratio. A comparative cost analysis also confirmed O₃/UV/H₂O₂ as the optimal configuration among similar AOPs, both in terms of efficiency and cost.[12]

Pulse electro-coagulation (PE)

Pulse electro-coagulation using iron (Fe) electrodes demonstrated notable efficiency in treating BRB-laden wastewater. Under optimal parameters, reaction time 3.5 h, duty cycle 0.3, pulse frequency 1 kHz, current density ∼19.44 mA cm-2, electrode spacing 2 cm, the method achieved 72.8% BRB removal and 69.6% chemical oxygen demand (COD) reduction. When applied to real wastewater, performance improved to 90.1% BRB removal (COD reduction: 62.6%). Significantly, PE consumed 90% less energy than conventional electro-coagulation (EC).[26]

Biological treatment: UASB–MBR hybrid system

A hybrid treatment combining an upflow anaerobic sludge blanket (UASB) with a membrane bioreactor (MBR) has demonstrated remarkable removal efficiencies for BRB. In synthetic wastewater, both BRB and COD removal consistently reached up to 99%, with NH₄+-N removal also at 98%. Notably, the system adapted to BRB-induced microbial shifts, enriching resistant or functional species such as Acinetobacter, Clostridium, Sphingomonas, Methylocystis, and Flavobacterium.[27]

Adsorption-based methods

Metal–Organic Framework (MOF), MIL-101(Fe): When applied in acidic BRB-containing wastewater, MIL-101(Fe) exhibited strong adsorption capability, with a maximum capacity of 163.93 mg g-1 at pH 7. Adsorption followed a pseudo-second-order kinetic model, and analysis suggested that π–π interactions primarily governed the BRB–MOF adsorption process, with no chemical transformation occurring.[25]

Polymeric Resins (e.g., H103): Researchers studied the adsorption of BRB by polymeric resin H103, focusing on kinetics and thermodynamics, though the summary did not provide specific removal metrics.[28]

Three-dimensional photoelectrocatalytic (3-D PEC) system

This advanced system employs a synergistic catalyst setup using Fe₂O₃/graphite and TiO₂-coated glass beads within a three-dimensional electrode architecture. At pH 3, it achieved 93% removal of berberine chloride form, 98.6% COD removal, 79% mineralization, and an energy cost of 3.16 kWh g-1 TOC within 120 min. Detection techniques (ESR, scavenging assays) identified superoxide radicals (O₂•–),

hydroxyl radicals (•OH), and photogenerated holes (h+) as the primary reactive species, with sulfate radicals playing a negligible role. The system demonstrates enhanced electron–hole separation and catalytic Fenton-like cycles for efficient pollutant mineralization.[29]

Hybrid anaerobic–aerobic Bioreactor: ABR-AGS process

Combining an anaerobic baffled reactor (ABR) with aerobic granular sludge (AGS) treatment has shown effectiveness in BRB degradation. In synthetic wastewater containing 120 mg L-1 BRB, the treatment removed 92.2% of BRB and 94.8% of COD. Microbial analysis identified specific functional species in both ABR and AGS units, including Bacillus endophyticus and various uncultured bacterial clones, which adapted to BRB exposure and facilitated its biodegradation.[30]

PHOTOCATALYSIS METHOD FOR THE REMOVAL OF WATER POLLUTION

Photocatalysis is an advanced oxidation process that has emerged as an environmentally friendly method for removing water pollutants, particularly organic contaminants, dyes, pharmaceuticals, and certain heavy metals. This method leverages the power of light, typically ultraviolet (UV) or visible light, to activate a semiconductor photocatalyst, most commonly titanium dioxide (TiO₂). However, researchers have also employed other materials, such as zinc oxide (ZnO), tungsten trioxide (WO₃), and various doped nanomaterials.[31] Photocatalysis fundamentally relies on light energy exciting electrons within the photocatalyst when the energy of the incident light equals or exceeds the photocatalyst’s bandgap. This excitation causes electrons to jump from the valence band to the conduction band, leaving behind positively charged “holes” in the valence band. These photogenerated electron-hole pairs initiate a cascade of redox reactions when they interact with water and dissolved oxygen molecules in the aqueous environment. The holes can oxidize water or hydroxide ions to produce highly reactive hydroxyl radicals (•OH), while the electrons reduce oxygen to form superoxide radicals (O₂•−). Both reactive oxygen species (ROS) are potent oxidizing agents that can decompose complex organic pollutants into less harmful end products, such as carbon dioxide, water, and inorganic ions.[32] A significant advantage of photocatalysis is that it does not require the addition of harmful chemicals, making it a clean technology with minimal secondary pollution. Additionally, it can simultaneously target a wide range of contaminants, which is highly advantageous for treating complex wastewater.[33] However, despite its many benefits, photocatalysis still faces several challenges that limit its practical, large-scale application. These include the need for efficient photocatalysts that can operate under visible light, issues related to catalyst recovery and reusability, and the recombination of electron-hole pairs, which reduces overall efficiency. To overcome these limitations, ongoing research focuses on developing novel photocatalysts with enhanced activity, such as those modified with noble metals, carbon-based materials, or heterojunction structures.[33]

Catalytic degradation of BRB

The catalytic degradation of BRB using environmentally friendly metal oxide NPs represents a promising strategy for its removal from wastewater.[34,35] This section will focus on the application of these nanomaterials for BRB degradation, exploring the mechanisms involved, influencing factors, and reported findings. While specific studies focusing solely on the degradation of BRB using exclusively environmentally friendly synthesized Metal Oxide Nanoparticles (MONPs) might be an emerging area, research employing MONPs synthesized through various routes provides valuable insights into their potential. Furthermore, studies on the degradation of other structurally similar alkaloids or model pharmaceutical compounds using eco-friendly MONPs can offer relevant information.

Factors influencing catalytic efficiency

Various factors related to the catalyst, the pollutant, and the reaction conditions govern the efficiency of catalytic degradation of BH using environmentally friendly MONPs.[36] We provide a more detailed exploration of these factors below.

Surface area and porosity: A higher surface area provides more active sites for adsorption and reaction, thereby generally enhancing catalytic activity. The pore size distribution can influence the accessibility of the catalyst surface to BRB molecules.[37]

Crystalline structure and phase: For photocatalytic MONPs such as TiO₂ and ZnO, the crystalline phase strongly influences their band gap energy, charge separation efficiency, and, consequently, their photocatalytic activity. For example, studies often report that anatase TiO₂ exhibits higher activity than rutile.[38]

Particle size and morphology: NPs with smaller sizes exhibit a larger surface-to-volume ratio, enhancing reactivity. The morphology (e.g., NPs, nanorods, nanosheets) can also influence the number of exposed active sites and light harvesting efficiency in photocatalysis.[39]

Surface defects and composition: Surface defects can act as trapping sites for photogenerated electrons and holes, influencing charge recombination rates in photocatalysis. The presence of specific surface functional groups or dopants can modify the electronic properties and catalytic activity of MONPs.[40]

Stability and resistance to leaching: The catalyst should be stable under the reaction conditions and exhibit minimal leaching of metal ions into the treated water to prevent secondary pollution.[41]

Catalyst dosage: Increasing the catalyst dosage generally increases the number of active sites, leading to a higher degradation rate up to an optimal point. Beyond this optimal dosage, several factors can lead to a decrease in efficiency, including:

Light scattering and shielding (for photocatalysis): Excessive catalyst concentration can increase solution turbidity, reducing light penetration and thus the activation of photocatalytic NPs .[42]

Particle agglomeration: High nanoparticle concentrations can promote agglomeration, reducing the effective surface area available for reaction.

Increased scavenging of reactive species: At very high catalyst loadings, the reactive species generated might react with the catalyst surface itself or with other NPs, reducing their availability for pollutant degradation.[43]

Initial BRB concentration: The degradation kinetics of BRB often depend on its initial concentration. At low concentrations, the reaction typically follows pseudo-first-order kinetics, where the degradation rate is directly proportional to the BRB concentration.[44]

At higher initial concentrations, the active sites on the catalyst surface might become saturated, leading to a slower degradation rate and deviation from first-order kinetics. The reaction might then approach zero-order kinetics, where the degradation rate becomes independent of the BRB concentration.[45]

pH of the solution: pH significantly influences the surface charge of MONPs (e.g., the point of zero charge, pzc) and the speciation of BRB. The adsorption of BRB onto the catalyst surface is strongly affected by the electrostatic interactions between the charged surface and the ionic form of BRB, which is pH-dependent.[46] In photocatalytic processes, pH can affect the generation and lifetime of ROS. For example, the formation of hydroxyl radicals is often optimal under slightly acidic to neutral conditions.

In Fenton-like reactions using iron oxides, pH plays a critical role in generating hydroxyl radicals, with optimal activity typically observed in the acidic pH range (pH 2.5-3.5).[47]

Temperature: For most chemical reactions, increasing the temperature generally increases the reaction rate according to the Arrhenius equation (Eq. 1), which also holds for catalytic degradation processes, up to a specific limit at which catalyst stability might become an issue.[48,49] However, for photocatalytic reactions, the primary activation step involves light absorption, and the effect of temperature on the initial generation of electron-hole pairs might be less pronounced. Temperature can still influence subsequent surface reactions and ROS kinetics.

(1)
k = A e − E a R T

k is the rate constant (frequency of collisions resulting in a reaction), T is the absolute temperature, and A is the pre-exponential factor or Arrhenius factor or frequency factor. Arrhenius initially considered A to be a temperature-independent constant for each chemical reaction. However, more recent treatments include some temperature dependence, where Ea is the molar activation energy for the reaction, and R is the universal gas constant.

Light irradiation (for photocatalysis): The wavelength of the incident light must be equal to or shorter than the wavelength corresponding to the band gap energy of the semiconductor photocatalyst to initiate the generation of electron-hole pairs.[40]

The intensity of the light source directly affects the number of photons incident on the catalyst surface and, consequently, the rate of electron-hole pair generation, leading to a higher degradation rate at higher light intensities, up to a point where saturation may occur.[50]

Presence of oxidants: The concentration of oxidants like H2O2, persulfate, or peroxymonosulfate is a critical parameter in Fenton-like and sulfate radical-based AOPs.[51] An optimal oxidant concentration is usually required to maximize the generation of reactive radicals. Insufficient oxidant concentration limits radical production, whereas excessive oxidant concentration can lead to scavenging reactions that consume radicals, thereby reducing degradation efficiency.[52]

Presence of co-pollutants and water matrix components: Real wastewater contains a complex mixture of organic and inorganic substances that can interfere with the catalytic degradation of target pollutants, such as BRB.[53]

Competition for active sites: Other organic pollutants or natural organic matter (NOM) can compete with BRB for adsorption sites on the catalyst surface, reducing the availability of BRB for degradation.

Scavenging of reactive species: Inorganic ions (e.g., carbonates, bicarbonates, chlorides, sulfates) present in water can act as scavengers for the generated reactive radicals, reducing their effectiveness in degrading BRB.[43]

Turbidity and light Attenuation: Suspended solids and colored substances in wastewater can increase turbidity, hindering light penetration in photocatalytic processes and reducing catalyst activation.[54]

Catalyst poisoning or fouling: Certain components in the water matrix can adsorb strongly onto the catalyst surface, blocking active sites and leading to catalyst deactivation or fouling.[55]

Photocatalytic degradation mechanism of BRB

Photocatalysis is a widely studied advanced oxidation process (AOP) in which semiconductor NPs absorb light, generating electron-hole pairs that drive redox reactions for pollutant degradation.[56] The reaction mechanism follows these steps:

  • 1.

    Photon Absorption and Electron Excitation

    MO + h ν → MO e − + h +

  • 2.

    Reactive Oxygen Species (ROS) Formation

    H 2 ​ O + h + → • OH + H + O 2 ​ + e − → O 2 • ​

  • 3.

    Degradation of BRB

    • OH + BRB → Degradation Products  CO 2 ​ ,   H 2 ​ O ,   and inorganic ions

The hydroxyl radicals (•OH) and superoxide anions (O₂•–) produced during this process break down complex organic molecules into simpler, non-toxic compounds, making photocatalysis an effective method for BRB degradation.[43]

Role of nanotechnology in wastewater treatment

Nanotechnology plays a transformative role in wastewater treatment by offering highly efficient, selective, and cost-effective solutions for removing a broad spectrum of contaminants, including heavy metals, organic pollutants, pathogens, and emerging micropollutants such as pharmaceuticals and personal care products. The use of nanomaterials such as carbon nanotubes (CNTs), graphene oxide, metal-organic frameworks (MOFs), zero-valent metals (like nanoscale zero-valent iron), and various metal oxide NPs (MONPs) (like TiO₂, ZnO, and Fe₃O₄) has significantly enhanced the capabilities of conventional treatment technologies through improved adsorption, catalysis, disinfection, and membrane filtration processes.[57]

These nanomaterials possess unique physicochemical properties, including a high surface area-to-volume ratio, tunable surface chemistry, high reactivity, and the ability to be engineered for specific functions, making them ideal for targeting and removing contaminants at the molecular level. For instance, nanoscale adsorbents can efficiently capture heavy metals such as lead, arsenic, and mercury, while photocatalytic nanomaterials can degrade organic pollutants under light exposure into harmless by-products. Additionally, nanotechnology has revolutionized membrane filtration systems by introducing nanocomposite membranes with enhanced permeability, fouling resistance, and selectivity, significantly improving the performance of ultrafiltration, nanofiltration, and reverse osmosis systems.[58]

Antimicrobial NPs, such as silver or copper NPs, are also used to disinfect wastewater by effectively inactivating bacteria, viruses, and other pathogens. Furthermore, nanotechnology enables real-time monitoring and sensing of water quality by developing nanosensors that detect pollutants at extremely low concentrations. Despite its vast potential, the application of nanotechnology in wastewater treatment must address several challenges, including environmental and health risks associated with nanoparticle release, issues related to large-scale production, and cost-effectiveness. Nevertheless, continued research and development in this field are paving the way for safer, more sustainable, and highly efficient nanotechnology-based wastewater treatment systems that can meet the growing demands of water quality and environmental protection in both developed and developing regions.[59]

Potential of TiO₂ NPs for catalytic degradation

Titanium MONPs, particularly TiO₂, hold immense potential for catalytic degradation of environmental pollutants due to their exceptional photocatalytic properties, chemical stability, non-toxicity, and strong oxidative power. These NPs have been widely researched and utilized in the degradation of a wide range of organic contaminants, including dyes, pesticides, pharmaceuticals, and industrial effluents, especially in wastewater treatment applications.[60]

When exposed to ultraviolet or even visible light (in the case of doped or modified TiO₂), the semiconductor structure of TiO₂ is activated, generating electron-hole pairs that react with water and oxygen molecules in the surrounding environment to form highly reactive species like hydroxyl radicals (•OH) and superoxide anions (O₂•−). These radicals can break down complex organic molecules into harmless end products, such as carbon dioxide and water, thereby detoxifying the water without producing secondary pollutants.[61]

The nanoscale form of TiO₂ greatly enhances its surface area, increasing the number of active sites available for catalytic reactions and improving overall degradation efficiency. Moreover, the surface of TiO₂ NPs can be engineered or doped with other elements (e.g., nitrogen, silver, or graphene) to enhance their visible-light activity, reduce electron-hole recombination, and improve photocatalytic performance under solar irradiation.[62]

These properties make TiO₂ NPs especially promising for sustainable, low-cost, and energy-efficient environmental remediation strategies. Despite their significant advantages, practical applications still face challenges related to catalyst recovery, reuse, and potential nanoparticle toxicity or environmental leaching.[63] However, advancements in immobilization techniques, magnetic separation, and nanocomposite development are addressing these issues, paving the way for titanium oxide-based nanocatalysts to play a central role in advanced oxidation processes for environmental cleanup, particularly in treating persistent organic pollutants in contaminated water systems.[64]

Green chemistry

In the face of increasing global environmental challenges and the growing demand for sustainable development, the field of chemistry has undergone a significant transformation over the past few decades. This transformation is epitomized by the emergence and advancement of green chemistry, a revolutionary approach that seeks to design chemical products and processes that reduce or eliminate the use and generation of hazardous substances. Green Chemistry, often referred to as sustainable chemistry, is a proactive, innovative framework that addresses environmental issues at the molecular level, encouraging scientists, researchers, industries, and policymakers to integrate environmental consciousness into the very foundations of chemical design and production.[65]

The traditional practices of chemistry, while pivotal in the development of modern society, have also contributed to a host of environmental and health problems, including toxic waste generation, resource depletion, pollution, and climate change. Conventional chemical processes often rely on non-renewable resources, produce harmful by-products, and require extensive energy input. These consequences have prompted an urgent need for alternative approaches that are both environmentally benign and economically viable. Green Chemistry emerged in the 1990s as a response to these concerns, aiming to shift the paradigm from remediation and control to prevention and sustainability.[66]

Green Chemistry was formally defined by Paul T. Anastas and John C. Warner, who articulated its 12 guiding principles in their groundbreaking book Green Chemistry: Theory and Practice (1998). These principles serve as the foundation for designing safer chemicals and processes, emphasizing waste minimization, energy efficiency, the use of renewable feedstocks, atom economy, and inherently safer design. For instance, instead of cleaning up toxic spills after the fact, green chemistry encourages the development of non-toxic alternatives in the first place, an approach that aligns with the well-known adage, “prevention is better than cure”.[67]

One of the most profound impacts of green chemistry is its interdisciplinary nature. It intersects with areas such as environmental science, chemical engineering, materials science, toxicology, and even economics and policy-making. This interdisciplinary approach enables the creation of innovative solutions that address complex environmental problems without compromising industrial productivity or technological advancement. From biodegradable plastics and non-toxic solvents to catalytic processes and energy-efficient reactions, green chemistry is reshaping the way chemicals are synthesized, used, and disposed of.[68]

Moreover, green chemistry plays a critical role in achieving global sustainability goals. It supports the United Nations’ Sustainable Development Goals (SDGs), particularly those related to clean water and sanitation (Goal 6), responsible consumption and production (Goal 12), climate action (Goal 13), and life on land and underwater (Goals 14 and 15). By reducing the ecological footprint of chemical industries and promoting safer alternatives, Green Chemistry directly contributes to environmental protection and public health while also stimulating economic growth through innovation and green technologies.[69]

In industrial applications, the adoption of green chemistry principles has led to remarkable achievements. Many companies have re-engineered their manufacturing processes to be more sustainable, resulting in reduced costs, enhanced safety, and improved regulatory compliance. For example, the development of solvent-free reactions, bio-based materials, and clean synthesis routes has enabled industries to reduce their reliance on petroleum-derived chemicals and their environmental impact. Pharmaceutical companies, in particular, have embraced green chemistry to improve the efficiency and environmental profile of drug synthesis, reducing waste and the use of harmful reagents.[70]

Education and public awareness are also crucial components of the green chemistry movement. Universities and academic institutions around the world have begun to integrate green chemistry into their curricula, training a new generation of chemists who are not only scientifically proficient but also environmentally responsible. Initiatives such as the green chemistry Commitment and various national and international conferences are fostering a global community dedicated to advancing sustainable chemical practices.[71]

Despite its many successes, the widespread implementation of green chemistry still faces challenges. These include technological limitations, economic barriers, lack of awareness, and resistance to change within traditional industrial frameworks. However, continued research, supportive policy development, and collaboration between academia, industry, and government can accelerate the adoption of green chemistry principles across all sectors of society (Scheme 1).[72]

Schematic diagram for green synthesis of MONPs.
Scheme 1
Schematic diagram for green synthesis of MONPs.

The biomolecules present in plant extracts, including alkaloids, flavonoids, tannins, and phenolics, play a key role in controlling particle size, shape, and stability, resulting in NPs with enhanced physicochemical and catalytic properties. This green route not only simplifies the synthesis process but also significantly reduces environmental impact and energy consumption.[73]

The plant-mediated synthesis of MONPs, such as TiO₂, has shown remarkable potential for applications including water purification, antimicrobial treatments, and photocatalysis, owing to the biocompatibility and functional versatility of the resulting nanomaterials.[74]

General survey for the preparation of TiO₂ NPs using plant extract

In recent years, green synthesis of MONPs has emerged as a highly promising, environmentally sustainable alternative to conventional chemical and physical methods.[75] Among various metal oxides, TiO₂ NPs has gained significant attention due to its exceptional properties, including high photocatalytic activity, chemical stability, non-toxicity, and wide-ranging applications in environmental remediation, solar energy conversion, antimicrobial coatings, cosmetics, and biomedicine.[76]

Traditional synthesis routes, however, often involve toxic precursors, high energy consumption, and hazardous by-products, raising concerns regarding their environmental impact and cost-effectiveness. In response to these challenges, researchers have increasingly turned to plant-mediated synthesis, also known as phytofabrication, as a green and sustainable approach. Plant extracts serve as natural reducing and stabilizing agents, offering a rich reservoir of bioactive compounds such as alkaloids, phenolics, flavonoids, terpenoids, and saponins, which facilitate the controlled synthesis of TiO₂ NPs under mild conditions.[77]

This survey provides a comprehensive overview of recent advances in the biosynthesis of TiO₂ NPs using a wide variety of plant sources, including leaves, seeds, flowers, roots, and fruit peels. It highlights the diversity of plant species used, the influence of phytochemical composition on nanoparticle morphology and crystallinity, and the wide range of functional applications reported in the literature [Table 1].

Table 1: Plant-mediated synthesis of TiO2 NPs.
Plant extract Extract type Shape Application Ref.
Kniphofia foliosa Aqueous Spherical drug-resistant bacteria [78]
Cassia fistula Aqueous Spherical Antibacterial [79]
Averrhoa bilimbi Aqueous Spherical antimicrobial and methylene blue degradation [80]
Carica papaya Aqueous Spherical dye degradation [81]
Trianthema portulacastrum Aqueous Spherical antimicrobial and antioxidant [82]
Jatropha curcas Aqueous spherical/tetragonal degradation of tannery wastewater [83]
Azadirachta indica Aqueous/Ethanolic Spherical antimicrobial [84]
Alcea and Thyme Aqueous spherical/irregular methylene blue degradation [85]
Jasmine flowers Aqueous Spherical dye-sensitized solar cell [86]
Lagenaria siceraria Aqueous Irregular photo-degradation of rg-19 dye [87]
Phyllanthus niruri Aqueous Spherical antimicrobial agent [88]
Commelina benghalensis Aqueous/Ethanolic spherical/agglomerated methylene blue degradation [89]
Wrightia tinctoria Aqueous Spherical antifungal and antibacterial [90]
Nerium aragona Aqueous Spherical antibacterial [91]

Scirpoides holoschoenus 

Scirpoides holoschoenus, a perennial sedge commonly found in wetland and Mediterranean habitats, represents a novel and unexplored candidate for the green synthesis of TiO₂ NPs. To date, there are no published reports on the use of this species for nanoparticle fabrication, highlighting its potential as an innovative source of phytochemicals capable of reducing and stabilizing metal oxides. Rich in bioactive compounds such as flavonoids, phenolics, and terpenoids common in many Cyperaceae family members S. holoschoenus may offer a sustainable, eco-friendly alternative for synthesizing TiO₂ NPs with controlled morphology and enhanced functionality.[90] Leveraging this plant could open new directions in green nanotechnology, particularly for applications in photocatalysis, environmental remediation, and biomedicine, while also promoting the use of underutilized native flora in advanced materials science.

This perennial sedge of the Cyperaceae family is indeed present in Saudi Arabia, forming part of the country’s wetland and riparian flora. Its native distribution spans the Arabian Peninsula, including Saudi Arabia and Yemen.[91] Field specimens have been documented at several locations within the kingdom: one collected approximately 6 km north of Al Bahah along the Taif–Jiddah road at an elevation of around 7,000 ft (∼2,100 m); another from Wadi Hismah, below the Al Masane mine on the Abha–Najran road at about 5,000 ft (∼1,500 m); and one more found north of Abha, about 115 km away.

Though detailed ecological descriptions specific to Saudi Arabia are limited, the presence of these specimens suggests that the species favors montane or submontane habitats with some moisture, such as seasonal streams or wet depressions, in contrast to the surrounding arid or semi-arid landscape. These highland areas, including the Asir region, typically receive more precipitation and harbor more diverse vegetation, which aligns with the sedge’s usual preference for damp or marshy environments.[92]

Scirpoides holoschoenus has been shown to possess pharmacological properties, such as antioxidant, antimicrobial, and anti-inflammatory effects, that have been clearly attributed to this species. Its primary known uses are ecological, such as in wetland restoration or erosion control, and occasionally in traditional crafts like basketry. However, due to its environmental resilience, it holds potential for future research into possible medicinal or bioactive properties, primarily through phytochemical screening.[93]

Role of Scirpoides holoschoenus extract in the synthesis of TiO2 NPs

Phytochemical investigations of Scirpoides holoschoenus roots and rhizomes have identified a suite of natural products, including 21 stilbenes, six flavonoids, six ferulic acid derivatives, and four diterpenes, several of which are previously undescribed. Significant among these are the monoprenylated flavonoid sophoraflavanone B, and stilbene oligomers like trans-scirpusin B, scirpusin A, cassigarol E, cyperusphenol B/D, passiflorinol A, cyperusphenol A, and mesocyperusphenol A, some of which demonstrated strong inhibitory effects on the spore germination of Botrytis cinerea, a phytopathogen at concentrations as low as 0.35–0.53 mM.[94]

In green synthesis methods for TiO₂ NPs using plant extracts, it is well documented that plant-derived phytochemicals, especially flavonoids, phenolics, terpenoids, alkaloids, and tannins, serve as effective reducing and stabilizing (capping) agents, enabling the controlled formation of NPs while avoiding harsh chemicals.[95] The bioactive compounds present in Scirpoides holoschoenus, particularly its flavonoids, stilbenes (a type of phenolic), and diterpenes, suggest that extracts from this sedge could likewise mediate the green synthesis of TiO₂ NPs. These compounds could function to reduce titanium precursors and stabilize the resulting NPs, potentially allowing control over particle size, crystallinity, and surface properties.

CONCLUSION

This review shows that BRB is a new pharmaceutical contaminant that requires advanced, targeted remediation because it persists for long periods, is hazardous, and is difficult to remove with standard treatment methods. The manuscript demonstrates that metal oxide photocatalysts, particularly plant-mediated green-synthesized TiO₂, offer a promising avenue for efficient and sustainable BRB degradation, owing to their adjustable surface, structural, and optical characteristics. Building on the proven effectiveness of plant extracts rich in flavonoids, phenolics, and other reductive phytochemicals, this study identifies Scirpoides holoschoenus as an underutilized native resource in Saudi Arabia that could be used as a safe reducing and capping agent for the synthesis of TiO₂ NPs, which connects the need for wastewater treatment with local biodiversity and green chemistry principles. Future research should focus on the systematic optimization of TiO₂ synthesis from S. holoschoenus, comprehensive mechanistic and toxicity investigations in realistic water matrices, and scale-up evaluations incorporating life-cycle and techno-economic analyses to advance green-synthesized photocatalysts toward practical applications in pharmaceutical wastewater treatment.

Author’s contribution

AA: Literature search and collection, data curation, initial draft preparation, figure design, manuscript writing-original draft; SA: Conceptualization, supervision, manuscript review and editing, critical revision; MT: Conceptualization, supervision, manuscript review and editing, critical revision; SS: Conceptualization, project administration, supervision, manuscript review and editing.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

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