Water Cleaning through Nanotechnology Systems

In our minds, water symbolizes life, thus its tangible presence is secondary to its symbolic meaning. Sustainable clean water supplies are essential to global health, ecology, and economy. Humanity is facing a tremendous challenge in meeting rising demands of potable water as freshwater supplies are decreasing due to extended droughts, population growth, decline in water quality, especially groundwater due to increasing groundwater and surface water pollution, unabated flooding, and increasing demands from competing users. As a natural resource, human necessity, and national asset, water requires proper planning, development, and management. Over the last several decades, population growth and surface and groundwater overexploitation have caused water shortages worldwide. Wastewater is rising and polluting freshwater reserves without effective treatment and management.

Urbanization has been on the rise, and this has been causing the amount of water used on a per capita basis to rise in towns and cities. As a result, it is necessary to acknowledge the need of managing the water reserves that are now available in order to prevent the occurrence of water scarcity in the future. The availability of clean drinking water is something that people are concerned about these days. Groundwater is by far the most significant water resource for the nation when it comes to fulfilling practically all of its water demands. According to a research conducted by the United Nations Environment Programme (UNEP), more than two billion people all over the world rely on aquifers as their source of drinking water. (United Nations Environment Programme, 2013) Irrigated agriculture, which depends mostly on groundwater, is responsible for the production of forty percent of the food consumed worldwide. (United Nations Environment Programme, 2013)

Groundwater makes up 95% of freshwater on Earth (excluding the polar ice caps), making it essential to human survival and economic progress. The growing scarcity of groundwater and declining water quality have put the people, particularly rural communities, at risk and compelled everyone to treat groundwater since pure water is becoming scarce. The globe is experiencing a groundwater shortage due to uncontrolled consumption. The only way to go from "groundwater development" to "groundwater management" is to optimize groundwater use for long-term sustainability. Today, everyone must offer safe drinking water, thus water treatment procedures must be simple, cost-effective, and long-lasting.

The diverse geological, climatological, and geographical makeup of India creates distinct groundwater circumstances in different regions. Groundwater purity is threatened by unsustainable resource usage and indiscriminate pesticide, fertilizer, and industrial pollution use. Agrochemicals, residential, and industrial waste pollute shallow aquifers. Microbes (intestinal pathogens and viruses), nutrients (phosphates and nitrates), heavy metals and metalloids (arsenic, lead, mercury), organic compounds (DDT, lubricants, industrial solvents), oil, sediments, and heat are major water pollutants. Byproducts of most industrial and goods-producing activity are pollutants. Heavy metals from the groundwater may bioaccumulate in human and animal tissues. In India and Bangladesh, almost 100 million people live in arsenic-contaminated areas. 9 of 19 West Bengal districts, 78 blocks, and 3150 villages have arsenic-contaminated groundwater. (Battacharya et al., 2022) It takes years for contaminants to reach aquifers, but once they do, they are hard and expensive to remove. Over 80% of sewage in poor nations is untreated, polluting rivers, lakes, and coastal waters. (UNESCO, 2019)

Nanotechnology offers an advanced and effective approach to water purification by using nanoscale materials with high surface area and strong reactivity, enabling the efficient removal of contaminants such as heavy metals, microorganisms, and organic pollutants (Savage & Diallo, 2015). Various nanomaterials including metal nanoparticles, metal oxides, carbon-based structures, and polymeric systems play a vital role in adsorption, photocatalysis, and disinfection processes that enhance water treatment performance (Borrego et al., 2016; Chen et al., 2016). Despite these advantages, challenges remain regarding environmental safety, potential toxicity, cost, and regulatory limitations that influence large-scale implementation (Mamadou & Savage, 2015). This review highlights current applications and future prospects of nanotechnology in water purification, emphasizing the increasing importance of sustainable and innovative nano-enabled solutions for providing safe and clean water.

Nanoparticles remediate more material faster and with fewer byproducts than granular forms because to their large surface area and reactivity. Nanosorbents, nanocatalysts, bioactive nanoparticles, nanostructured catalytic membranes, nanotubes, magnetic nanoparticles, granules, flake, high surface area metal particle supramolecular assemblies with characteristic length scales of 9-10 nm, including clusters, micromolecules, nanoparticles, and colloids, may solve many water quality issues. (Mamadou & Savage, 2015) Nanoparticles' versatility in water remediation stems from their modest particle sizes (1-100 nm) compared to bacterial cells (1 μm). Groundwater can transport nanoparticles efficiently. They can suspend for long enough to launch an in situ therapy sphere. Thus, nanoparticles may be fixed onto a solid matrix like activated carbon or zeolite to improve water treatment.

One of the most promising areas for solving the problems of water pollution and shortage on a worldwide scale is nanotechnology. The key to its success is nanoscale material engineering, which allows for vast improvements in adsorption capacity, surface area, reactivity, and catalytic behavior. Heavy metals, infections, dyes, pharmaceuticals, and organic pollutants can be quickly and selectively removed from a system using nanomaterials like metals, metal oxides, carbon-based structures, and polymeric nanoparticles, which outperform their bulk equivalents (Savage & Diallo, 2015). Nanoparticles may be efficiently disseminated in water, transported across porous surfaces, and incorporated into modern purification systems due to their very tiny size.

Several processes, such as adsorption, photocatalysis, membrane filtration, redox reactions, and antimicrobial activity, are used by water purification systems that are based on nanotechnology. The photocatalytic characteristics of zinc oxide and titanium dioxide nanoparticles degrade organic pollutants when exposed to ultraviolet light, and the antibacterial actions of silver nanoparticles against various microorganisms are well-known (Borrego et al., 2016). In a similar vein, metal-based nanoparticles like nano-zero-valent iron (nZVI) may undergo oxidation-reduction processes to transform heavy metals and chlorinated compounds, among other hazardous substances, into less dangerous versions (Xiong et al., 2015). When compared to more conventional methods of water treatment, nanotechnology's superior processes make it the clear winner.

In addition, the creation of the next generation of filtration systems, such as nanocomposite membranes, carbon nanotube membranes, and purification materials that have been strengthened with graphene, is made possible by the use of nanotechnology. The permeability, selectivity, and resistance to fouling that these membranes demonstrate are excellent, which paves the way for techniques of water treatment that are both highly efficient and energy-saving (Ying et al., 2017). In addition, the overall efficacy, economic efficiency, and sustainability of traditional treatment methods have been enhanced by the use of nanoparticles. Nanotechnology is becoming increasingly seen as a transformational instrument with the capacity to solve complicated water quality problems and to satisfy the worldwide need for drinking water that is both clean and safe. This is due to the continuous development of research in the field.

Metal Nanoparticles

Silver Nanoparticles: Nanoparticles of silver are very poisonous to many types of bacteria, viruses, and fungus, and they have a powerful antibacterial effect. (Da Silva et al., 2016) Silver nanoparticles are effective water disinfectants due to their antibacterial characteristics. Modern water treatment systems make effective use of silver nanoparticles as a disinfectant. The antimicrobial properties and cost-effectiveness of filter materials incorporated with silver nanoparticles make them a popular choice for water disinfection, even though their efficacy in long-term use is reduced and they tend to aggregate in aqueous mediums. (Quang et al., 2013) Because of their antifouling and disinfecting properties, membranes or ceramic materials doped with silver nanoparticles have been widely employed for the treatment of domestic water over the last twenty years. One example is ceramic filters that may improve E. coli removal effectiveness by using clay and adding silver nanoparticles. Additionally, it was shown that filters with a higher porosity tend to eliminate germs more effectively than filters with a lower porosity. Reportedly, the addition of silver nanoparticles improved the filter's effectiveness and led to a 97.8% and 100% rise in the E. coli removal rates, respectively. (Oyanedel-Craver and Smith, 2018)

Iron Nanoparticles: The superior absorption and reducing characteristics that are shown by nano zero valent iron (nZVI) may be attributed to the tiny size and vast surface area of the nZVI. These characteristics render these nano zero valent iron (nZVI) efficient agents for the elimination of a wide variety of pollutants, including halogenated and nitrogenous chemicals, dyes, phenols, inorganic ions, heavy metals, and radioactive components. (Xiong, Zhang, and Li, 2015) The moment these nano zero valent iron (nZVI) and pollutants come into contact, an oxidation-reduction process occurs, resulting in the oxidation of Fe2+ to Fe3+. Consequently, ferric hydroxide, Fe(OH)3, is produced, and this compound makes the elimination of heavy hazardous metals easier. (Wang, Chen, and Wang, 2014)

Metal Oxides Nanoparticles

Titanium oxide Nanoparticles (TiO2 NPs): To remove pollutants from wastewater, the photocatalytic degradation process is currently the gold standard. The photocatalytic activity, stability, and low cost of titanium oxide nanoparticles make them a useful catalyst. The catalysts oxidize pollutants into low molecular weight products such as CO2, H2O, NO3 -, Cl, etc., when they come into contact with them. (Guesh et al., 2016) described to break down heavy metals, cyanides, polycyclic aromatic hydrocarbons, chlorinated organic chemicals, dyes, and phenols, titanium oxide nanoparticles are used as selective degrading agents. (Chen et al., 2016) Additionally, these nanoparticles are powerful antimicrobials that can kill a broad variety of viruses, fungus, bacteria, and gram-negative and gram-positive bacteria. One further approach that shows promise for solving the titanium oxide nanoparticle recovery issue is the coupling technology of TiO2 NPs with membranes such polyamide-imide, polymethyl methacrylate, polyvinylidene fluoride, or polyethersulfone (Rajesh et al., 2013). Titanium oxide nanoparticles may be readily separated by a simple filtering process because to this interaction.

Zinc Oxide Nanoparticles (ZnO NPs): Zinc oxide nanoparticles are also particularly effective photocatalysis agents for the treatment of wastewater, which is attributable to their unique properties, such as band gap in the near-UV spectral area and oxidizing power. These nanoparticles are appropriate for the treatment of wastewater due to their biocompatibility. (Schmidt-Mende and MacManus-Driscoll, 2017)

Iron Oxides Nanoparticles: Iron oxide nanoparticles are often utilized these days to remove heavy metals due to the fact that they are easy to produce and are simple in nature. As a result of their very diminutive size, it is customary to extract nano sorbent materials from water that has been polluted. However, because of their magnetic properties, magnetite and maghemite are able to be used as adsorbents. It is possible to recover these iron oxide nanoparticles from solution by applying an external magnetic field to them because of their magnetic properties. As a result, these nanoparticles may be used as nanosorbants. As a result, the nanoparticles in question are performing in an exceptional manner as nanosorbents for the purpose of eliminating heavy metal ions from water.

Carbon Nanotubes (CNT)

The structural and electrical characteristics of carbon nanomaterials (CNMs) make them intriguing candidates for the role of adsorption agents. Carbon nanomaterials offer an advantage in the treatment of wastewater due to their huge surface area and their selective nature for aromatics. In comparison to other carbon nanomaterials, carbon nanotubes (CNTs) are more effectively used as a result of their structure. Carbon nanotubes (CNTs) have been shown to have a particular adsorption capacity for a number of substances, including cations, dyes, and ethyl benzene. It is possible to increase the adsorption capacity of CNTs by functionalizing them, which in turn increases the surface area and dispensability of the CNTs. (Adeleye et al., 2016), nanocomposite adsorbents are able to remove chromium from water. These adsorbents are created by combining carbon nanotubes (CNTs) with magnetic characteristics and iron oxide with adsorption capabilities.

Nanocomposites

Among the nanomaterials that are now available, nanocomposites are the most prominent because of their magnetic qualities, which also make it simple to separate them from the solution. (Azari et al., 2024) The incorporation of titanium oxide nanoparticles, together with the production of a co-polyamide network on a polyimide backing, makes it possible to build a nano filtration membrane. In addition, nanocomposites possess a particular binding capability via chelation and ion exchange, and they play an active role in the many forms that they take, including polymer nanocomposites, carbon nanocomposites, and metal oxide nanocomposites.

Dendrimers

Dendrimers are separate three-dimensional macromolecules with a symmetric core, an inner shell, and an outer shell. They are monodispersed and nanosized. Dendrimers are useful in materials engineering because they may be used as nanoscale building blocks to create more complicated nano-structured materials. To improve the rate of recovery of various metal ions from water, dendrimers may also be functionalized with other materials. Another usage for dendrimers is in water treatment, where they may act as chemical sensors and remove heavy metals. When it comes to water filtration, dendrimers are great for absorbing harmful heavy metal ions since they are water soluble ligands. The flow diagram in Figure 1 may be used to depict many nanomaterials.

Figure 1: Different Nanomaterials used in water purification

Organic nanoparticles

Due to elemental carbon's structural and changing hybridization state, organic nanostructures exhibit unique electrical, chemical, and physical capabilities. SWCNTs, MWCNTs, graphene, carbon dots, fullerene C60, and C540 are the main nano-structural forms of carbon. Organic nanoparticles are schematically shown in Figure 2. Carbon dots (CDs) are popular nanomaterials because of their biocompatibility, low toxicity, abundance of raw materials, and inexpensive cost. CDs are sub-10-nm quasi-spherical carbon nanoparticles (NPs). CDs' outstanding surface qualities, chemical resilience, water solubility, and luminescence have made them famous. (Ajith et al., 2020) Decontamination requires surface modification and activation of carbon nanoparticles. These usages mainly include SWNT, MWNT, and graphene. These nanoparticles are one of the finest at adsorbing organic and inorganic contaminants in polluted water. Physisorption and chemisorption occur during surface alteration and manufacturing. Along with adsorption, photocatalysis cleans water. Titanium oxide nanoparticles coupled with graphene improve photocatalysis compared to alone. (Zhang et al., 2020)

Figure 2: Types of organic nanoparticles

Inorganic nanoparticles

In the field of water remediation, the most significant inorganic nanoparticle is metal and metal oxide nanoparticles (M&MO NPs). This category covers a variety of nanoparticles, including titanium dioxide nanoparticles (TiO2 NPs), silver nanoparticles (Ag NPs), iron and iron oxide nanoparticles (Fe and FeO NPs), copper oxide nanoparticles (CuO NPs), and silica nanoparticles. (Bashambu and colleagues, 2021) Heavy metals as well as chlorinated organic water contaminants are adsorbed with great efficacy by M&MNO nanoparticles. Due to the quick kinetics, adsorption capacity, and flexibility to adapt to both in-situ and ex-situ applications, M&MO nanoparticles are inescapable in the process of cleanup, especially in watery settings. There has been a great deal of interest in the area of decontamination in mesoporous silica nanoparticles (SiO2 NPs) that have pore sizes that range from two to fifty nanometers. Because they can be functionalized on the surface with simplicity and because their pore width may be adjusted, silicon dioxide nanoparticles are ideal for a wide variety of applications. (Santhosh, Raghavendra, and Bhat, 2016) The presence of -OH groups on SiO2 nanoparticles makes it possible to modify the surface and assist in the process of removing a broad range of contaminants.

Polymeric nanoparticles

Particle stability is a limitation of nanoparticles, despite their many benefits, as we have shown. A large body of research suggests that, after production, nanoparticles may assemble under certain conditions. Aggregation of particles reduces their adsorption ability. One possible substitute might be polymeric NPs. To prevent NP agglutination and enhance the stability of pure nanoparticles, we use a matrix or backing material to hold them in place. The polymeric host includes stabilizing agents, emulsifiers, surfactants, and ligands that modify surfaces. Nanoparticles (NPs) made of polymers typically have a size range of 1–1000 nm. Heavy metals (Fe, Hg, Mn, As), organic pollutants (pesticides, pharmaceuticals, VOCs, other aliphatic and aromatic compounds), gases (SO2, CO2, NO2), and microbes (bacteria, viruses, and other pathogens) are just some of the contaminants that polymeric NPs can detect and remove. (Tsekhmistrenko et al., 2020) The most promising membrane technologies among the various suggested ones are composites, self-assembled two-dimensional layer materials, aligned nanotube membranes, tightly packed nanoparticle and nanofiber membranes, and aligned nanotube membranes. (Ying et al., 2017)

Environmental Impact and Human Health Concerns:

Potential Release of Nanomaterials into the Environment: The possible discharge of nanoparticles into the environment is a major worry about using nanotechnology for water purification. Nanomaterials pose a threat to aquatic environments due to their potential for accidental release during manufacturing, use, and disposal. These nanoparticles have the potential to amass in the environment if they are not well controlled. This might have disastrous effects. Several environmental problems, such as bioaccumulation, ecological disturbance, and toxicity to aquatic creatures, may emerge from the discharge of nanomaterials. (Ghosh & Chen, 2020) There is concern that nanoparticles might have negative impacts on aquatic ecosystems and other parts of the environment due to their interactions with numerous environmental components.

Long-Term Effects on Human Health and Ecosystems: It is yet unclear what impact nanomaterial exposure will have on ecosystems and human health in the long run. No one knows for sure how nanoparticles will affect people's health or the environment, and studies into their possible toxicity are continuing. There are concerns about the possible dangers of nanoparticles since they may interact with the body differently and exhibit different behaviors than bigger particles of the same substance. (Qu, Alvarez & Li, 2013)

There is a chance that treated water may include small quantities of nanoparticles if water filtration methods using nanomaterials are used. Concerns about possible hazards to human health have been raised by the prolonged intake of water contaminated with nanomaterials. Furthermore, these nanoparticles have the ability to interfere with naturally occurring ecological equilibrium by interacting with beneficial microbes and aquatic life. To address these issues, we need more studies on nanomaterials' environmental destiny, behavior, and toxicity and more responsible waste management techniques to keep them out of the environment as little as possible.

Scalability and Cost-Effectiveness

Considerations for Practical Implementation of Nanotechnology-Based Systems: The use of nanomaterials in water purification has tremendous potential, but there are scaling issues that will need to be addressed before they can be put into practice outside of the lab. Scaling up the production of nanomaterials while keeping their quality constant may be an arduous and expensive process. For nanoparticles to be used in water treatment systems, it is essential that they can be mass-produced in an efficient and trustworthy manner. (Zhang & Chen, 2021) In addition, much preparation and thought are required for incorporating nanotechnology into preexisting water treatment infrastructures or developing brand-new systems. To guarantee smooth integration and long-term sustainability, it is necessary to assess feasibility, cost-effectiveness, and compatibility with standard treatment techniques.

Addressing Scalability and Cost-Related Challenges: Concerned parties in the research and business communities are relentlessly looking for solutions to the scaling and pricing issues plaguing water filtration systems that use nanotechnology. To enable large-scale production, new approaches to nanomaterial synthesis are being explored, including scalable manufacturing methods and continuous flow procedures. Optimizing the performance of nanomaterials, decreasing the amount of nanoparticles needed for successful treatment, and improving their reusability to lower operating costs are further goals being pursued. To discover creative ways to tackle scalability and cost-effectiveness issues, it is essential for academics, businesses, and regulatory agencies to work together. (Qu, Alvarez & Li, 2013)

Standardization and Regulations

Importance of Standardized Characterization Techniques: Standardized characterization procedures are crucial for guaranteeing the dependable and uniform performance of nanomaterials in water purification. Precise and uniform measurements of nanomaterial characteristics, including dimensions, morphology, surface chemistry, and stability, are essential for understanding their behavior in water treatment procedures. (Ghosh & Chen, 2020) The absence of defined characterization methodologies may result in inconsistencies in research outcomes and impede meaningful comparisons across various nanomaterials. The establishment of standardized standards for nanomaterial characterization is essential to enhance transparency and enable information exchange.

Ensuring Safe and Sustainable Deployment of Nanomaterials in Water Treatment: It is crucial to create thorough laws and standards to ensure the safe and long-term use of nanomaterials in water treatment. To safeguard human and environmental health from nanomaterials, appropriate regulation is becoming more important as the area of nanotechnology develops further. Guidelines for the disposal of trash containing nanomaterials, environmental risk assessments, and allowed quantities of nanomaterials in treated water are all important components of any regulatory framework. Building confidence and ensuring responsible implementation of water purification systems based on nanotechnology requires open and honest communication among all parties involved, including the public, scientists, and lawmakers. (Chen & Zhang, 2019)

Although nanotechnology has immense potential in solving water purification problems, it also brings substantial obstacles that must be handled with caution. Careful investigation and responsible management of nanomaterials in water treatment is required to address concerns about their effects on the environment, potential hazards to human health, scalability, cost-effectiveness, and regulation. The safe and long-term use of nanotechnology in water purification relies on the combined efforts of researchers, legislators, and industry players. Communities across the globe may benefit greatly from water treatment systems that use nanomaterials if thorough research is conducted, new solutions are implemented, and strong regulatory frameworks are put in place.

Nanotechnology is anticipated to have a progressively significant role in tackling worldwide water purification concerns in the next years. As research progresses, novel nanomaterials exhibiting enhanced efficiency, selectivity, and stability are being formulated to eliminate a broader spectrum of pollutants from water. These technologies have the capacity to enhance the speed, efficacy, and cost-effectiveness of water treatment for both urban and rural populations.

A significant rising theme is the development of ecologically sustainable or "green" nanomaterials. These materials are engineered to be biodegradable, non-toxic, and sustainable, hence mitigating the dangers linked to conventional nanoparticles. Green nanotechnology seeks to integrate superior purifying efficacy with less environmental repercussions, positioning it as a potential strategy for future water treatment systems.

The development of intelligent nanomaterials that are capable of reacting to fluctuations in the state of the water is another area of potential. These materials have the ability to detect contaminants, modify their activity, and even renew themselves while they are being used. As a result, the life expectancy of filtration systems is extended, and the frequency with which they need to be replaced is reduced, which in turn reduces the total expenses of treatment. Nanotechnology is also anticipated to be a major factor in the improvement of systems for the purification of membranes. There is a possibility that future nanocomposite membranes may provide greater permeability, less fouling, and more durable properties than their traditional counterparts. The implementation of these developments has the potential to increase the efficiency and energy conservation of large-scale desalination and wastewater treatment processes.

The amalgamation of nanotechnology with digital technologies, including sensors, automation, and artificial intelligence, is creating novel avenues for real-time monitoring and intelligent purifying systems. These sophisticated devices might assist communities in promptly detecting pollution, preserving water quality, and guaranteeing clean drinking water consistently.  Ultimately, ongoing research and development will probably result in broader commercial accessibility of nano-enabled purifying systems. With advancements in manufacturing processes and reductions in prices, nanotechnology solutions may become available to families, industries, and rural regions, aiding worldwide initiatives to provide clean and safe water for all.

Nanotechnology presents a possible avenue for enhanced, efficient, and sustainable water purification technologies. The varied array of nanomaterials, including metals, metal oxides, carbon-based structures, composites, and polymers, has considerable promise in eliminating pollutants that conventional approaches find challenging to address. Notwithstanding the benefits, factors such as toxicity, environmental hazards, financial implications, and insufficient regulatory frameworks need careful evaluation. Ongoing research, innovation, and appropriate use will be crucial to fully exploit the promise of nanotechnology for access to clean water. With ongoing breakthroughs in materials and technology, nano-enabled purification systems are expected to become more feasible, safe, and extensively used in the future.