Pollution and adsorption techniques
Cellulose-based materials and their modified forms as adsorbents for the removal of dyes and toxic heavy metals from wastewater.
The adsorbent’s adsorption ability is increased by lowering the cellulose size to the nanoscale.
The quality of water resources is worsening day by day due to several anthropogenic activities, increasing industrial development and unplanned expansion.
Dyes are complex organic compounds that are eliminated from various industrial sources such as textile, cosmetic, paper, leather, rubber and printing industries to color their products.
Dye-bearing effluent is a significant source of water pollution.
Human activities have also resulted in substantial quantities of heavy metals being free into the hydrosphere causing Ecotoxicological hazards due to their tendency to accumulate in vital organs and high toxicity.
Water containing dyes and heavy metals causes a potential hazard to the environment and human health.
Water pollution
Water pollution is a big issue that affects people all around the world. Heavy metals and dyes are major pollutants that cause many problems to the health of humans and ecosystems.
Several treatment technologies are available to reduce the effects of pollutants.
These problems push the world to have a green method that is more efficient, cost-effective and environment-friendly for water purification.
Adsorption is recognized as a green, clean, and adaptable wastewater treatment technology.
Cellulose-based materials attained considerable attention for water purification because of their easily available, biodegradable and non-toxic nature.
Treatment Methods
Many treatment methods have been developed for water purification.
These include chemical precipitation, ion exchange, coagulation-flocculation, membrane separation, electrochemical treatment and adsorption.
Adsorption is found to be effective, cheap, simple and relatively lower the operation cost of dye removal.
Different types of materials have been developed as adsorbents for the effective adsorption of pollutants.
Adsorption is a fast, cheap, and widely used method as it can be applied for the removal of a wide spectrum of soluble and insoluble contaminants and biological pollutants with high removal efficiency.
Moreover, its high efficiency in pollutant removal without the production of toxic by-products makes adsorption one of the most popular methods for water refinement.
The process of adsorption is a mass transfer process involving the transfer of a substance from the solution phase and resulting in the deposition at the surface of the other phase.
The substance being adsorbed is termed the adsorbate and the adsorbing surface is called adsorbent.
If the interaction between the adsorbate and the adsorbent is due to the weak van der Waal’s forces, then the process is physisorption or physical adsorption.
Defiantly, if the attraction forces between the adsorbate and adsorbent are due to chemical bonding, then chemisorption.
The general mechanism of adsorption involves the transfer of the contaminant from the bulk solution to the outer surface of the adsorbent.
Ideal materials to be green adsorbents
The ideal materials for the adsorption of pollutants should meet several requirements
such as:
_Mechanical and good structural integrity to overcome water flow for a long time.
_High adsorption capacities with high rates.
_Have a large surface area and possess a regeneration aptitude using cost-effective approaches.
The main advantage of adsorption:
_The use of low-cost materials with satisfactory adsorption properties and environmentally-friendly nature.
_As per these requirements, nowadays researchers are switching to green adsorbents due to their abundance, biodegradability, and non-toxic nature.
Green adsorbents
Under this term, green adsorbents include low-cost materials originating from:
_Natural sources
_Agricultural residues and wastes particularly lignocellulosic biomass
_Low-cost sources from which activated carbon adsorbents will be produced.
These green adsorbents were found to be lower in terms of their adsorption capacity than commercial adsorbents such as modified chitosan, activated adsorbents, structurally-complex inorganic composite materials, etc., but their cost potential makes them competitive.
Cellulosic adsorbents have the proficiency to meet almost all the requirements for being green.
With responsible and thoughtful research, development and deployment, cellulosic materials have the potential to become sustainable, green materials of choice for high-end applications such as water purification.
References
[1] Grégorio Crini, Eric Lichtfouse, Green Adsorbents for Pollutant Removal: Fundamentals and Design, Volume 18 of Environmental Chemistry for a Sustainable World, Springer, 2018.
